mirror of https://github.com/python/cpython
165 lines
6.8 KiB
ReStructuredText
165 lines
6.8 KiB
ReStructuredText
.. highlight:: c
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.. _string-conversion:
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String conversion and formatting
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================================
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Functions for number conversion and formatted string output.
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.. c:function:: int PyOS_snprintf(char *str, size_t size, const char *format, ...)
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Output not more than *size* bytes to *str* according to the format string
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*format* and the extra arguments. See the Unix man page :manpage:`snprintf(3)`.
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.. c:function:: int PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
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Output not more than *size* bytes to *str* according to the format string
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*format* and the variable argument list *va*. Unix man page
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:manpage:`vsnprintf(3)`.
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:c:func:`PyOS_snprintf` and :c:func:`PyOS_vsnprintf` wrap the Standard C library
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functions :c:func:`snprintf` and :c:func:`vsnprintf`. Their purpose is to
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guarantee consistent behavior in corner cases, which the Standard C functions do
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not.
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The wrappers ensure that ``str[size-1]`` is always ``'\0'`` upon return. They
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never write more than *size* bytes (including the trailing ``'\0'``) into str.
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Both functions require that ``str != NULL``, ``size > 0``, ``format != NULL``
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and ``size < INT_MAX``. Note that this means there is no equivalent to the C99
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``n = snprintf(NULL, 0, ...)`` which would determine the necessary buffer size.
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The return value (*rv*) for these functions should be interpreted as follows:
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* When ``0 <= rv < size``, the output conversion was successful and *rv*
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characters were written to *str* (excluding the trailing ``'\0'`` byte at
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``str[rv]``).
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* When ``rv >= size``, the output conversion was truncated and a buffer with
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``rv + 1`` bytes would have been needed to succeed. ``str[size-1]`` is ``'\0'``
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in this case.
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* When ``rv < 0``, "something bad happened." ``str[size-1]`` is ``'\0'`` in
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this case too, but the rest of *str* is undefined. The exact cause of the error
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depends on the underlying platform.
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The following functions provide locale-independent string to number conversions.
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.. c:function:: unsigned long PyOS_strtoul(const char *str, char **ptr, int base)
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Convert the initial part of the string in ``str`` to an :c:expr:`unsigned
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long` value according to the given ``base``, which must be between ``2`` and
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``36`` inclusive, or be the special value ``0``.
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Leading white space and case of characters are ignored. If ``base`` is zero
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it looks for a leading ``0b``, ``0o`` or ``0x`` to tell which base. If
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these are absent it defaults to ``10``. Base must be 0 or between 2 and 36
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(inclusive). If ``ptr`` is non-``NULL`` it will contain a pointer to the
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end of the scan.
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If the converted value falls out of range of corresponding return type,
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range error occurs (:c:data:`errno` is set to :c:macro:`!ERANGE`) and
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:c:macro:`!ULONG_MAX` is returned. If no conversion can be performed, ``0``
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is returned.
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See also the Unix man page :manpage:`strtoul(3)`.
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.. versionadded:: 3.2
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.. c:function:: long PyOS_strtol(const char *str, char **ptr, int base)
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Convert the initial part of the string in ``str`` to an :c:expr:`long` value
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according to the given ``base``, which must be between ``2`` and ``36``
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inclusive, or be the special value ``0``.
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Same as :c:func:`PyOS_strtoul`, but return a :c:expr:`long` value instead
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and :c:macro:`LONG_MAX` on overflows.
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See also the Unix man page :manpage:`strtol(3)`.
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.. versionadded:: 3.2
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.. c:function:: double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception)
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Convert a string ``s`` to a :c:expr:`double`, raising a Python
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exception on failure. The set of accepted strings corresponds to
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the set of strings accepted by Python's :func:`float` constructor,
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except that ``s`` must not have leading or trailing whitespace.
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The conversion is independent of the current locale.
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If ``endptr`` is ``NULL``, convert the whole string. Raise
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:exc:`ValueError` and return ``-1.0`` if the string is not a valid
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representation of a floating-point number.
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If endptr is not ``NULL``, convert as much of the string as
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possible and set ``*endptr`` to point to the first unconverted
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character. If no initial segment of the string is the valid
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representation of a floating-point number, set ``*endptr`` to point
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to the beginning of the string, raise ValueError, and return
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``-1.0``.
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If ``s`` represents a value that is too large to store in a float
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(for example, ``"1e500"`` is such a string on many platforms) then
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if ``overflow_exception`` is ``NULL`` return ``Py_INFINITY`` (with
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an appropriate sign) and don't set any exception. Otherwise,
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``overflow_exception`` must point to a Python exception object;
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raise that exception and return ``-1.0``. In both cases, set
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``*endptr`` to point to the first character after the converted value.
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If any other error occurs during the conversion (for example an
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out-of-memory error), set the appropriate Python exception and
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return ``-1.0``.
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.. versionadded:: 3.1
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.. c:function:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)
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Convert a :c:expr:`double` *val* to a string using supplied
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*format_code*, *precision*, and *flags*.
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*format_code* must be one of ``'e'``, ``'E'``, ``'f'``, ``'F'``,
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``'g'``, ``'G'`` or ``'r'``. For ``'r'``, the supplied *precision*
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must be 0 and is ignored. The ``'r'`` format code specifies the
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standard :func:`repr` format.
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*flags* can be zero or more of the values ``Py_DTSF_SIGN``,
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``Py_DTSF_ADD_DOT_0``, or ``Py_DTSF_ALT``, or-ed together:
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* ``Py_DTSF_SIGN`` means to always precede the returned string with a sign
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character, even if *val* is non-negative.
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* ``Py_DTSF_ADD_DOT_0`` means to ensure that the returned string will not look
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like an integer.
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* ``Py_DTSF_ALT`` means to apply "alternate" formatting rules. See the
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documentation for the :c:func:`PyOS_snprintf` ``'#'`` specifier for
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details.
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If *ptype* is non-``NULL``, then the value it points to will be set to one of
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``Py_DTST_FINITE``, ``Py_DTST_INFINITE``, or ``Py_DTST_NAN``, signifying that
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*val* is a finite number, an infinite number, or not a number, respectively.
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The return value is a pointer to *buffer* with the converted string or
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``NULL`` if the conversion failed. The caller is responsible for freeing the
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returned string by calling :c:func:`PyMem_Free`.
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.. versionadded:: 3.1
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.. c:function:: int PyOS_stricmp(const char *s1, const char *s2)
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Case insensitive comparison of strings. The function works almost
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identically to :c:func:`!strcmp` except that it ignores the case.
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.. c:function:: int PyOS_strnicmp(const char *s1, const char *s2, Py_ssize_t size)
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Case insensitive comparison of strings. The function works almost
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identically to :c:func:`!strncmp` except that it ignores the case.
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