mirror of https://github.com/python/cpython
131 lines
5.0 KiB
ReStructuredText
131 lines
5.0 KiB
ReStructuredText
.. highlightlang:: 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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.. cfunction:: 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(2)`.
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.. cfunction:: 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(2)`.
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:cfunc:`PyOS_snprintf` and :cfunc:`PyOS_vsnprintf` wrap the Standard C library
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functions :cfunc:`snprintf` and :cfunc:`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`` and ``format !=
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NULL``.
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If the platform doesn't have :cfunc:`vsnprintf` and the buffer size needed to
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avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a
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*Py_FatalError*.
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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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.. cfunction:: double PyOS_ascii_strtod(const char *nptr, char **endptr)
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Convert a string to a :ctype:`double`. This function behaves like the Standard C
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function :cfunc:`strtod` does in the C locale. It does this without changing the
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current locale, since that would not be thread-safe.
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:cfunc:`PyOS_ascii_strtod` should typically be used for reading configuration
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files or other non-user input that should be locale independent.
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See the Unix man page :manpage:`strtod(2)` for details.
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.. cfunction:: char * PyOS_ascii_formatd(char *buffer, size_t buf_len, const char *format, double d)
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Convert a :ctype:`double` to a string using the ``'.'`` as the decimal
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separator. *format* is a :cfunc:`printf`\ -style format string specifying the
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number format. Allowed conversion characters are ``'e'``, ``'E'``, ``'f'``,
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``'F'``, ``'g'`` and ``'G'``.
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The return value is a pointer to *buffer* with the converted string or NULL if
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the conversion failed.
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.. deprecated:: 3.1
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Use :cfunc:`PyOS_double_to_string` instead.
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.. cfunction:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)
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Convert a :ctype:`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'``, ``'g'``,
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``'G'``, ``'s'``, or ``'r'``. For ``'s'`` and ``'r'``, the supplied
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*precision* must be 0 and is ignored. These specify the standard
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:func:`str` and :func:`repr` formats, respectively.
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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 :cfunc:`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 :cfunc:`PyMem_Free`.
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.. versionadded:: 3.1
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.. cfunction:: double PyOS_ascii_atof(const char *nptr)
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Convert a string to a :ctype:`double` in a locale-independent way.
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See the Unix man page :manpage:`atof(2)` for details.
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.. cfunction:: char * PyOS_stricmp(char *s1, char *s2)
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Case insensitive comparison of strings. The function works almost
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identically to :cfunc:`strcmp` except that it ignores the case.
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.. cfunction:: char * PyOS_strnicmp(char *s1, 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 :cfunc:`strncmp` except that it ignores the case.
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