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