mirror of https://github.com/python/cpython.git
94 lines
3.5 KiB
ReStructuredText
94 lines
3.5 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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.. 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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