EQStream abstraction layer

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.. _string-formatting-api:
*************
API Reference
*************
All functions and classes provided by the fmt library reside
in namespace ``fmt`` and macros have prefix ``FMT_``. For brevity the
namespace is usually omitted in examples.
Format API
==========
The following functions use :ref:`format string syntax <syntax>` similar
to the one used by Python's `str.format
<http://docs.python.org/3/library/stdtypes.html#str.format>`_ function.
They take *format_str* and *args* as arguments.
*format_str* is a format string that contains literal text and replacement
fields surrounded by braces ``{}``. The fields are replaced with formatted
arguments in the resulting string.
*args* is an argument list representing arbitrary arguments.
.. _format:
.. doxygenfunction:: format(CStringRef, ArgList)
.. doxygenfunction:: operator""_format(const char *, std::size_t)
.. _print:
.. doxygenfunction:: print(CStringRef, ArgList)
.. doxygenfunction:: print(std::FILE *, CStringRef, ArgList)
.. doxygenclass:: fmt::BasicFormatter
:members:
Date and time formatting
------------------------
The library supports `strftime <http://en.cppreference.com/w/cpp/chrono/c/strftime>`_-like
date and time formatting::
#include "fmt/time.h"
std::time_t t = std::time(nullptr);
// Prints "The date is 2016-04-29." (with the current date)
fmt::print("The date is {:%Y-%m-%d}.", *std::localtime(&t));
The format string syntax is described in the documentation of
`strftime <http://en.cppreference.com/w/cpp/chrono/c/strftime>`_.
``std::ostream`` support
------------------------
The header ``fmt/ostream.h`` provides ``std::ostream`` support including
formatting of user-defined types that have overloaded ``operator<<``::
#include "fmt/ostream.h"
class Date {
int year_, month_, day_;
public:
Date(int year, int month, int day) : year_(year), month_(month), day_(day) {}
friend std::ostream &operator<<(std::ostream &os, const Date &d) {
return os << d.year_ << '-' << d.month_ << '-' << d.day_;
}
};
std::string s = fmt::format("The date is {}", Date(2012, 12, 9));
// s == "The date is 2012-12-9"
.. doxygenfunction:: print(std::ostream&, CStringRef, ArgList)
.. doxygenfunction:: fprintf(std::ostream&, CStringRef, ArgList)
Argument formatters
-------------------
It is possible to change the way arguments are formatted by providing a
custom argument formatter class::
// A custom argument formatter that formats negative integers as unsigned
// with the ``x`` format specifier.
class CustomArgFormatter :
public fmt::BasicArgFormatter<CustomArgFormatter, char> {
public:
CustomArgFormatter(fmt::BasicFormatter<char, CustomArgFormatter> &f,
fmt::FormatSpec &s, const char *fmt)
: fmt::BasicArgFormatter<CustomArgFormatter, char>(f, s, fmt) {}
void visit_int(int value) {
if (spec().type() == 'x')
visit_uint(value); // convert to unsigned and format
else
fmt::BasicArgFormatter<CustomArgFormatter, char>::visit_int(value);
}
};
std::string custom_format(const char *format_str, fmt::ArgList args) {
fmt::MemoryWriter writer;
// Pass custom argument formatter as a template arg to BasicFormatter.
fmt::BasicFormatter<char, CustomArgFormatter> formatter(args, writer);
formatter.format(format_str);
return writer.str();
}
FMT_VARIADIC(std::string, custom_format, const char *)
std::string s = custom_format("{:x}", -42); // s == "ffffffd6"
.. doxygenclass:: fmt::ArgVisitor
:members:
.. doxygenclass:: fmt::BasicArgFormatter
:members:
.. doxygenclass:: fmt::ArgFormatter
:members:
Printf formatting functions
---------------------------
The following functions use `printf format string syntax
<http://pubs.opengroup.org/onlinepubs/009695399/functions/fprintf.html>`_ with
a POSIX extension for positional arguments.
.. doxygenfunction:: printf(CStringRef, ArgList)
.. doxygenfunction:: fprintf(std::FILE *, CStringRef, ArgList)
.. doxygenfunction:: sprintf(CStringRef, ArgList)
Write API
=========
.. doxygenclass:: fmt::BasicWriter
:members:
.. doxygenclass:: fmt::BasicMemoryWriter
:members:
.. doxygenclass:: fmt::BasicArrayWriter
:members:
.. doxygenfunction:: bin(int)
.. doxygenfunction:: oct(int)
.. doxygenfunction:: hex(int)
.. doxygenfunction:: hexu(int)
.. doxygenfunction:: pad(int, unsigned, Char)
Utilities
=========
.. doxygenfunction:: fmt::arg(StringRef, const T&)
.. doxygenfunction:: operator""_a(const char *, std::size_t)
.. doxygendefine:: FMT_CAPTURE
.. doxygendefine:: FMT_VARIADIC
.. doxygenclass:: fmt::ArgList
:members:
.. doxygenclass:: fmt::BasicStringRef
:members:
.. doxygenclass:: fmt::BasicCStringRef
:members:
.. doxygenclass:: fmt::Buffer
:protected-members:
:members:
System errors
=============
.. doxygenclass:: fmt::SystemError
:members:
.. doxygenclass:: fmt::WindowsError
:members:
.. _formatstrings:
Custom allocators
=================
The fmt library supports custom dynamic memory allocators.
A custom allocator class can be specified as a template argument to
:class:`fmt::BasicMemoryWriter`::
typedef fmt::BasicMemoryWriter<char, CustomAllocator> CustomMemoryWriter;
It is also possible to write a formatting function that uses a custom
allocator::
typedef std::basic_string<char, std::char_traits<char>, CustomAllocator> CustomString;
CustomString format(CustomAllocator alloc, fmt::CStringRef format_str,
fmt::ArgList args) {
CustomMemoryWriter writer(alloc);
writer.write(format_str, args);
return CustomString(writer.data(), writer.size(), alloc);
}
FMT_VARIADIC(CustomString, format, CustomAllocator, fmt::CStringRef)
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########
Contents
########
.. toctree::
:maxdepth: 2
usage
api
syntax
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Overview
========
**fmt** (formerly cppformat) is an open-source formatting library.
It can be used as a safe alternative to printf or as a fast
alternative to C++ IOStreams.
.. raw:: html
<div class="panel panel-default">
<div class="panel-heading">What users say:</div>
<div class="panel-body">
Thanks for creating this library. Its been a hole in C++ for a long time.
Ive used both boost::format and loki::SPrintf, and neither felt like the
right answer. This does.
</div>
</div>
.. _format-api:
Format API
----------
The replacement-based Format API provides a safe alternative to ``printf``,
``sprintf`` and friends with comparable or `better performance
<http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.
The `format string syntax <doc/latest/index.html#format-string-syntax>`_ is similar
to the one used by `str.format <http://docs.python.org/2/library/stdtypes.html#str.format>`_
in Python:
.. code:: c++
fmt::format("The answer is {}", 42);
The ``fmt::format`` function returns a string "The answer is 42". You can use
``fmt::MemoryWriter`` to avoid constructing ``std::string``:
.. code:: c++
fmt::MemoryWriter w;
w.write("Look, a {} string", 'C');
w.c_str(); // returns a C string (const char*)
The ``fmt::print`` function performs formatting and writes the result to a file:
.. code:: c++
fmt::print(stderr, "System error code = {}\n", errno);
The file argument can be omitted in which case the function prints to
``stdout``:
.. code:: c++
fmt::print("Don't {}\n", "panic");
If your compiler supports C++11, then the formatting functions are implemented
with variadic templates. Otherwise variadic functions are emulated by generating
a set of lightweight wrappers. This ensures compatibility with older compilers
while providing a natural API.
The Format API also supports positional arguments useful for localization:
.. code:: c++
fmt::print("I'd rather be {1} than {0}.", "right", "happy");
Named arguments can be created with ``fmt::arg``. This makes it easier to track
what goes where when multiple values are being inserted:
.. code:: c++
fmt::print("Hello, {name}! The answer is {number}. Goodbye, {name}.",
fmt::arg("name", "World"), fmt::arg("number", 42));
If your compiler supports C++11 user-defined literals, the suffix ``_a`` offers
an alternative, slightly terser syntax for named arguments:
.. code:: c++
fmt::print("Hello, {name}! The answer is {number}. Goodbye, {name}.",
"name"_a="World", "number"_a=42);
The ``_format`` suffix may be used to format string literals similar to Python:
.. code:: c++
std::string message = "{0}{1}{0}"_format("abra", "cad");
Other than the placement of the format string on the left of the operator,
``_format`` is functionally identical to ``fmt::format``. In order to use the
literal operators, they must be made visible with the directive
``using namespace fmt::literals;``. Note that this brings in only ``_a`` and
``_format`` but nothing else from the ``fmt`` namespace.
.. _write-api:
Write API
---------
The concatenation-based Write API (experimental) provides a
`fast <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_
stateless alternative to IOStreams:
.. code:: c++
fmt::MemoryWriter out;
out << "The answer in hexadecimal is " << hex(42);
.. _safety:
Safety
------
The library is fully type safe, automatic memory management prevents buffer overflow,
errors in format strings are reported using exceptions. For example, the code
.. code:: c++
fmt::format("The answer is {:d}", "forty-two");
throws a ``FormatError`` exception with description
"unknown format code 'd' for string", because the argument
``"forty-two"`` is a string while the format code ``d``
only applies to integers.
Where possible, errors are caught at compile time. For example, the code
.. code:: c++
fmt::format("Cyrillic letter {}", L'\x42e');
produces a compile-time error because wide character ``L'\x42e'`` cannot be
formatted into a narrow string. You can use a wide format string instead:
.. code:: c++
fmt::format(L"Cyrillic letter {}", L'\x42e');
For comparison, writing a wide character to ``std::ostream`` results in
its numeric value being written to the stream (i.e. 1070 instead of letter 'ю' which
is represented by ``L'\x42e'`` if we use Unicode) which is rarely what is needed.
.. _portability:
Portability
-----------
The library is highly portable. Here is an incomplete list of operating systems and
compilers where it has been tested and known to work:
* 64-bit (amd64) GNU/Linux with GCC 4.4.3, `4.6.3 <https://travis-ci.org/fmtlib/fmt>`_,
4.7.2, 4.8.1 and Intel C++ Compiler (ICC) 14.0.2
* 32-bit (i386) GNU/Linux with GCC 4.4.3, 4.6.3
* Mac OS X with GCC 4.2.1 and Clang 4.2, 5.1.0
* 64-bit Windows with Visual C++ 2010, 2013 and
`2015 <https://ci.appveyor.com/project/vitaut/fmt>`_
* 32-bit Windows with Visual C++ 2010
Although the library uses C++11 features when available, it also works with older
compilers and standard library implementations. The only thing to keep in mind
for C++98 portability:
* Variadic templates: minimum GCC 4.4, Clang 2.9 or VS2013. This feature allows
the Format API to accept an unlimited number of arguments. With older compilers
the maximum is 15.
* User-defined literals: minimum GCC 4.7, Clang 3.1 or VS2015. The suffixes
``_format`` and ``_a`` are functionally equivalent to the functions
``fmt::format`` and ``fmt::arg``.
The output of all formatting functions is consistent across platforms. In particular,
formatting a floating-point infinity always gives ``inf`` while the output
of ``printf`` is platform-dependent in this case. For example,
.. code::
fmt::print("{}", std::numeric_limits<double>::infinity());
always prints ``inf``.
.. _ease-of-use:
Ease of Use
-----------
fmt has a small self-contained code base consisting of a single header file
and a single source file and no external dependencies. A permissive BSD `license
<https://github.com/fmtlib/fmt#license>`_ allows using the library both
in open-source and commercial projects.
.. raw:: html
<a class="btn btn-success" href="https://github.com/fmtlib/fmt">GitHub Repository</a>
<div class="section footer">
<iframe src="http://ghbtns.com/github-btn.html?user=fmtlib&amp;repo=fmt&amp;type=watch&amp;count=true"
class="github-btn" width="100" height="20"></iframe>
</div>
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.. _syntax:
********************
Format String Syntax
********************
Formatting functions such as :ref:`fmt::format() <format>` and :ref:`fmt::print() <print>`
use the same format string syntax described in this section.
Format strings contain "replacement fields" surrounded by curly braces ``{}``.
Anything that is not contained in braces is considered literal text, which is
copied unchanged to the output. If you need to include a brace character in the
literal text, it can be escaped by doubling: ``{{`` and ``}}``.
The grammar for a replacement field is as follows:
.. productionlist:: sf
replacement_field: "{" [`arg_id`] [":" `format_spec`] "}"
arg_id: `integer` | `identifier`
integer: `digit`+
digit: "0"..."9"
identifier: `id_start` `id_continue`*
id_start: "a"..."z" | "A"..."Z" | "_"
id_continue: `id_start` | `digit`
In less formal terms, the replacement field can start with an *arg_id*
that specifies the argument whose value is to be formatted and inserted into
the output instead of the replacement field.
The *arg_id* is optionally followed by a *format_spec*, which is preceded
by a colon ``':'``. These specify a non-default format for the replacement value.
See also the :ref:`formatspec` section.
If the numerical arg_ids in a format string are 0, 1, 2, ... in sequence,
they can all be omitted (not just some) and the numbers 0, 1, 2, ... will be
automatically inserted in that order.
Some simple format string examples::
"First, thou shalt count to {0}" // References the first argument
"Bring me a {}" // Implicitly references the first argument
"From {} to {}" // Same as "From {0} to {1}"
The *format_spec* field contains a specification of how the value should be
presented, including such details as field width, alignment, padding, decimal
precision and so on. Each value type can define its own "formatting
mini-language" or interpretation of the *format_spec*.
Most built-in types support a common formatting mini-language, which is
described in the next section.
A *format_spec* field can also include nested replacement fields within it.
These nested replacement fields can contain only an argument index;
format specifications are not allowed. Formatting is performed as if the
replacement fields within the format_spec are substituted before the
*format_spec* string is interpreted. This allows the formatting of a value
to be dynamically specified.
See the :ref:`formatexamples` section for some examples.
.. _formatspec:
Format Specification Mini-Language
==================================
"Format specifications" are used within replacement fields contained within a
format string to define how individual values are presented (see
:ref:`syntax`). Each formattable type may define how the format
specification is to be interpreted.
Most built-in types implement the following options for format specifications,
although some of the formatting options are only supported by the numeric types.
The general form of a *standard format specifier* is:
.. productionlist:: sf
format_spec: [[`fill`]`align`][`sign`]["#"]["0"][`width`]["." `precision`][`type`]
fill: <a character other than '{' or '}'>
align: "<" | ">" | "=" | "^"
sign: "+" | "-" | " "
width: `integer` | "{" `arg_id` "}"
precision: `integer` | "{" `arg_id` "}"
type: `int_type` | "c" | "e" | "E" | "f" | "F" | "g" | "G" | "p" | "s"
int_type: "b" | "B" | "d" | "o" | "x" | "X"
The *fill* character can be any character other than '{' or '}'. The presence
of a fill character is signaled by the character following it, which must be
one of the alignment options. If the second character of *format_spec* is not
a valid alignment option, then it is assumed that both the fill character and
the alignment option are absent.
The meaning of the various alignment options is as follows:
+---------+----------------------------------------------------------+
| Option | Meaning |
+=========+==========================================================+
| ``'<'`` | Forces the field to be left-aligned within the available |
| | space (this is the default for most objects). |
+---------+----------------------------------------------------------+
| ``'>'`` | Forces the field to be right-aligned within the |
| | available space (this is the default for numbers). |
+---------+----------------------------------------------------------+
| ``'='`` | Forces the padding to be placed after the sign (if any) |
| | but before the digits. This is used for printing fields |
| | in the form '+000000120'. This alignment option is only |
| | valid for numeric types. |
+---------+----------------------------------------------------------+
| ``'^'`` | Forces the field to be centered within the available |
| | space. |
+---------+----------------------------------------------------------+
Note that unless a minimum field width is defined, the field width will always
be the same size as the data to fill it, so that the alignment option has no
meaning in this case.
The *sign* option is only valid for number types, and can be one of the
following:
+---------+----------------------------------------------------------+
| Option | Meaning |
+=========+==========================================================+
| ``'+'`` | indicates that a sign should be used for both |
| | positive as well as negative numbers. |
+---------+----------------------------------------------------------+
| ``'-'`` | indicates that a sign should be used only for negative |
| | numbers (this is the default behavior). |
+---------+----------------------------------------------------------+
| space | indicates that a leading space should be used on |
| | positive numbers, and a minus sign on negative numbers. |
+---------+----------------------------------------------------------+
The ``'#'`` option causes the "alternate form" to be used for the
conversion. The alternate form is defined differently for different
types. This option is only valid for integer and floating-point types.
For integers, when binary, octal, or hexadecimal output is used, this
option adds the prefix respective ``"0b"`` (``"0B"``), ``"0"``, or
``"0x"`` (``"0X"``) to the output value. Whether the prefix is
lower-case or upper-case is determined by the case of the type
specifier, for example, the prefix ``"0x"`` is used for the type ``'x'``
and ``"0X"`` is used for ``'X'``. For floating-point numbers the
alternate form causes the result of the conversion to always contain a
decimal-point character, even if no digits follow it. Normally, a
decimal-point character appears in the result of these conversions
only if a digit follows it. In addition, for ``'g'`` and ``'G'``
conversions, trailing zeros are not removed from the result.
.. ifconfig:: False
The ``','`` option signals the use of a comma for a thousands separator.
For a locale aware separator, use the ``'n'`` integer presentation type
instead.
*width* is a decimal integer defining the minimum field width. If not
specified, then the field width will be determined by the content.
Preceding the *width* field by a zero (``'0'``) character enables
sign-aware zero-padding for numeric types. This is equivalent to a *fill*
character of ``'0'`` with an *alignment* type of ``'='``.
The *precision* is a decimal number indicating how many digits should be
displayed after the decimal point for a floating-point value formatted with
``'f'`` and ``'F'``, or before and after the decimal point for a floating-point
value formatted with ``'g'`` or ``'G'``. For non-number types the field
indicates the maximum field size - in other words, how many characters will be
used from the field content. The *precision* is not allowed for integer,
character, Boolean, and pointer values.
Finally, the *type* determines how the data should be presented.
The available string presentation types are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'s'`` | String format. This is the default type for strings and |
| | may be omitted. |
+---------+----------------------------------------------------------+
| none | The same as ``'s'``. |
+---------+----------------------------------------------------------+
The available character presentation types are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'c'`` | Character format. This is the default type for |
| | characters and may be omitted. |
+---------+----------------------------------------------------------+
| none | The same as ``'c'``. |
+---------+----------------------------------------------------------+
The available integer presentation types are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'b'`` | Binary format. Outputs the number in base 2. Using the |
| | ``'#'`` option with this type adds the prefix ``"0b"`` |
| | to the output value. |
+---------+----------------------------------------------------------+
| ``'B'`` | Binary format. Outputs the number in base 2. Using the |
| | ``'#'`` option with this type adds the prefix ``"0B"`` |
| | to the output value. |
+---------+----------------------------------------------------------+
| ``'d'`` | Decimal integer. Outputs the number in base 10. |
+---------+----------------------------------------------------------+
| ``'o'`` | Octal format. Outputs the number in base 8. |
+---------+----------------------------------------------------------+
| ``'x'`` | Hex format. Outputs the number in base 16, using |
| | lower-case letters for the digits above 9. Using the |
| | ``'#'`` option with this type adds the prefix ``"0x"`` |
| | to the output value. |
+---------+----------------------------------------------------------+
| ``'X'`` | Hex format. Outputs the number in base 16, using |
| | upper-case letters for the digits above 9. Using the |
| | ``'#'`` option with this type adds the prefix ``"0X"`` |
| | to the output value. |
+---------+----------------------------------------------------------+
| ``'n'`` | Number. This is the same as ``'d'``, except that it uses |
| | the current locale setting to insert the appropriate |
| | number separator characters. |
+---------+----------------------------------------------------------+
| none | The same as ``'d'``. |
+---------+----------------------------------------------------------+
Integer presentation types can also be used with character and Boolean values.
Boolean values are formatted using textual representation, either ``true`` or
``false``, if the presentation type is not specified.
The available presentation types for floating-point values are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'a'`` | Hexadecimal floating point format. Prints the number in |
| | base 16 with prefix ``"0x"`` and lower-case letters for |
| | digits above 9. Uses 'p' to indicate the exponent. |
+---------+----------------------------------------------------------+
| ``'A'`` | Same as ``'a'`` except it uses upper-case letters for |
| | the prefix, digits above 9 and to indicate the exponent. |
+---------+----------------------------------------------------------+
| ``'e'`` | Exponent notation. Prints the number in scientific |
| | notation using the letter 'e' to indicate the exponent. |
+---------+----------------------------------------------------------+
| ``'E'`` | Exponent notation. Same as ``'e'`` except it uses an |
| | upper-case 'E' as the separator character. |
+---------+----------------------------------------------------------+
| ``'f'`` | Fixed point. Displays the number as a fixed-point |
| | number. |
+---------+----------------------------------------------------------+
| ``'F'`` | Fixed point. Same as ``'f'``, but converts ``nan`` to |
| | ``NAN`` and ``inf`` to ``INF``. |
+---------+----------------------------------------------------------+
| ``'g'`` | General format. For a given precision ``p >= 1``, |
| | this rounds the number to ``p`` significant digits and |
| | then formats the result in either fixed-point format |
| | or in scientific notation, depending on its magnitude. |
| | |
| | A precision of ``0`` is treated as equivalent to a |
| | precision of ``1``. |
+---------+----------------------------------------------------------+
| ``'G'`` | General format. Same as ``'g'`` except switches to |
| | ``'E'`` if the number gets too large. The |
| | representations of infinity and NaN are uppercased, too. |
+---------+----------------------------------------------------------+
| none | The same as ``'g'``. |
+---------+----------------------------------------------------------+
Floating-point formatting is locale-dependent.
.. ifconfig:: False
+---------+----------------------------------------------------------+
| | The precise rules are as follows: suppose that the |
| | result formatted with presentation type ``'e'`` and |
| | precision ``p-1`` would have exponent ``exp``. Then |
| | if ``-4 <= exp < p``, the number is formatted |
| | with presentation type ``'f'`` and precision |
| | ``p-1-exp``. Otherwise, the number is formatted |
| | with presentation type ``'e'`` and precision ``p-1``. |
| | In both cases insignificant trailing zeros are removed |
| | from the significand, and the decimal point is also |
| | removed if there are no remaining digits following it. |
| | |
| | Positive and negative infinity, positive and negative |
| | zero, and nans, are formatted as ``inf``, ``-inf``, |
| | ``0``, ``-0`` and ``nan`` respectively, regardless of |
| | the precision. |
| | |
+---------+----------------------------------------------------------+
The available presentation types for pointers are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'p'`` | Pointer format. This is the default type for |
| | pointers and may be omitted. |
+---------+----------------------------------------------------------+
| none | The same as ``'p'``. |
+---------+----------------------------------------------------------+
.. _formatexamples:
Format examples
===============
This section contains examples of the format syntax and comparison with
the printf formatting.
In most of the cases the syntax is similar to the printf formatting, with the
addition of the ``{}`` and with ``:`` used instead of ``%``.
For example, ``"%03.2f"`` can be translated to ``"{:03.2f}"``.
The new format syntax also supports new and different options, shown in the
following examples.
Accessing arguments by position::
format("{0}, {1}, {2}", 'a', 'b', 'c');
// Result: "a, b, c"
format("{}, {}, {}", 'a', 'b', 'c');
// Result: "a, b, c"
format("{2}, {1}, {0}", 'a', 'b', 'c');
// Result: "c, b, a"
format("{0}{1}{0}", "abra", "cad"); // arguments' indices can be repeated
// Result: "abracadabra"
Aligning the text and specifying a width::
format("{:<30}", "left aligned");
// Result: "left aligned "
format("{:>30}", "right aligned");
// Result: " right aligned"
format("{:^30}", "centered");
// Result: " centered "
format("{:*^30}", "centered"); // use '*' as a fill char
// Result: "***********centered***********"
Replacing ``%+f``, ``%-f``, and ``% f`` and specifying a sign::
format("{:+f}; {:+f}", 3.14, -3.14); // show it always
// Result: "+3.140000; -3.140000"
format("{: f}; {: f}", 3.14, -3.14); // show a space for positive numbers
// Result: " 3.140000; -3.140000"
format("{:-f}; {:-f}", 3.14, -3.14); // show only the minus -- same as '{:f}; {:f}'
// Result: "3.140000; -3.140000"
Replacing ``%x`` and ``%o`` and converting the value to different bases::
format("int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}", 42);
// Result: "int: 42; hex: 2a; oct: 52; bin: 101010"
// with 0x or 0 or 0b as prefix:
format("int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}", 42);
// Result: "int: 42; hex: 0x2a; oct: 052; bin: 0b101010"
.. ifconfig:: False
Using the comma as a thousands separator::
format("{:,}", 1234567890);
'1,234,567,890'
Expressing a percentage::
>>> points = 19
>>> total = 22
Format("Correct answers: {:.2%}") << points/total)
'Correct answers: 86.36%'
Using type-specific formatting::
>>> import datetime
>>> d = datetime.datetime(2010, 7, 4, 12, 15, 58)
Format("{:%Y-%m-%d %H:%M:%S}") << d)
'2010-07-04 12:15:58'
Nesting arguments and more complex examples::
>>> for align, text in zip('<^>', ['left', 'center', 'right']):
... '{0:{fill}{align}16}") << text, fill=align, align=align)
...
'left<<<<<<<<<<<<'
'^^^^^center^^^^^'
'>>>>>>>>>>>right'
>>>
>>> octets = [192, 168, 0, 1]
Format("{:02X}{:02X}{:02X}{:02X}") << *octets)
'C0A80001'
>>> int(_, 16)
3232235521
>>>
>>> width = 5
>>> for num in range(5,12):
... for base in 'dXob':
... print('{0:{width}{base}}") << num, base=base, width=width), end=' ')
... print()
...
5 5 5 101
6 6 6 110
7 7 7 111
8 8 10 1000
9 9 11 1001
10 A 12 1010
11 B 13 1011
+90
View File
@@ -0,0 +1,90 @@
*****
Usage
*****
To use the fmt library, add :file:`format.h` and :file:`format.cc` from
a `release archive <https://github.com/fmtlib/fmt/releases/latest>`_
or the `Git repository <https://github.com/fmtlib/fmt>`_ to your project.
Alternatively, you can :ref:`build the library with CMake <building>`.
If you are using Visual C++ with precompiled headers, you might need to add
the line ::
#include "stdafx.h"
before other includes in :file:`format.cc`.
.. _building:
Building the library
====================
The included `CMake build script`__ can be used to build the fmt
library on a wide range of platforms. CMake is freely available for
download from http://www.cmake.org/download/.
__ https://github.com/fmtlib/fmt/blob/master/CMakeLists.txt
CMake works by generating native makefiles or project files that can
be used in the compiler environment of your choice. The typical
workflow starts with::
mkdir build # Create a directory to hold the build output.
cd build
cmake <path/to/fmt> # Generate native build scripts.
where :file:`{<path/to/fmt>}` is a path to the ``fmt`` repository.
If you are on a \*nix system, you should now see a Makefile in the
current directory. Now you can build the library by running :command:`make`.
Once the library has been built you can invoke :command:`make test` to run
the tests.
If you use Windows and have Visual Studio installed, a :file:`FORMAT.sln`
file and several :file:`.vcproj` files will be created. You can then build them
using Visual Studio or msbuild.
On Mac OS X with Xcode installed, an :file:`.xcodeproj` file will be generated.
To build a `shared library`__ set the ``BUILD_SHARED_LIBS`` CMake variable to
``TRUE``::
cmake -DBUILD_SHARED_LIBS=TRUE ...
__ http://en.wikipedia.org/wiki/Library_%28computing%29#Shared_libraries
Building the documentation
==========================
To build the documentation you need the following software installed on your
system:
* `Python <https://www.python.org/>`_ with pip and virtualenv
* `Doxygen <http://www.stack.nl/~dimitri/doxygen/>`_
* `Less <http://lesscss.org/>`_ with less-plugin-clean-css
First generate makefiles or project files using CMake as described in
the previous section. Then compile the ``doc`` target/project, for example::
make doc
This will generate the HTML documentation in ``doc/html``.
Android NDK
===========
fmt provides `Android.mk file`__ that can be used to build the library
with `Android NDK <https://developer.android.com/tools/sdk/ndk/index.html>`_.
For an example of using fmt with Android NDK, see the
`android-ndk-example <https://github.com/fmtlib/android-ndk-example>`_
repository.
__ https://github.com/fmtlib/fmt/blob/master/Android.mk
Homebrew
========
fmt can be installed on OS X using `Homebrew <http://brew.sh/>`_::
brew install cppformat