Edit File: conversion.txt
.. highlightlang:: 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(2)`. .. 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(2)`. :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`` and ``format != NULL``. If the platform doesn't have :c:func:`vsnprintf` and the buffer size needed to avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a *Py_FatalError*. 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:: double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception) Convert a string ``s`` to a :c:type:`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 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:: 2.7 .. c:function:: double PyOS_ascii_strtod(const char *nptr, char **endptr) Convert a string to a :c:type:`double`. This function behaves like the Standard C function :c:func:`strtod` does in the C locale. It does this without changing the current locale, since that would not be thread-safe. :c:func:`PyOS_ascii_strtod` should typically be used for reading configuration files or other non-user input that should be locale independent. See the Unix man page :manpage:`strtod(2)` for details. .. versionadded:: 2.4 .. deprecated:: 2.7 Use :c:func:`PyOS_string_to_double` instead. .. c:function:: char* PyOS_ascii_formatd(char *buffer, size_t buf_len, const char *format, double d) Convert a :c:type:`double` to a string using the ``'.'`` as the decimal separator. *format* is a :c:func:`printf`\ -style format string specifying the number format. Allowed conversion characters are ``'e'``, ``'E'``, ``'f'``, ``'F'``, ``'g'`` and ``'G'``. The return value is a pointer to *buffer* with the converted string or NULL if the conversion failed. .. versionadded:: 2.4 .. deprecated:: 2.7 This function is removed in Python 2.7 and 3.1. Use :func:`PyOS_double_to_string` instead. .. c:function:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype) Convert a :c:type:`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:: 2.7 .. c:function:: double PyOS_ascii_atof(const char *nptr) Convert a string to a :c:type:`double` in a locale-independent way. See the Unix man page :manpage:`atof(2)` for details. .. versionadded:: 2.4 .. deprecated:: 3.1 Use :c:func:`PyOS_string_to_double` instead. .. c:function:: char* PyOS_stricmp(char *s1, char *s2) Case insensitive comparison of strings. The function works almost identically to :c:func:`strcmp` except that it ignores the case. .. versionadded:: 2.6 .. c:function:: char* PyOS_strnicmp(char *s1, 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. .. versionadded:: 2.6