182 lines
6.9 KiB
ReStructuredText
182 lines
6.9 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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.. 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(2)`.
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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(2)`.
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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`` and ``format !=
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NULL``.
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If the platform doesn't have :c:func:`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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.. 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:type:`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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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_HUGE_VAL`` (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:: 2.7
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.. c:function:: double PyOS_ascii_strtod(const char *nptr, char **endptr)
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Convert a string to a :c:type:`double`. This function behaves like the Standard C
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function :c:func:`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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:c:func:`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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.. versionadded:: 2.4
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.. deprecated:: 2.7
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Use :c:func:`PyOS_string_to_double` instead.
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.. c:function:: char* PyOS_ascii_formatd(char *buffer, size_t buf_len, const char *format, double d)
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Convert a :c:type:`double` to a string using the ``'.'`` as the decimal
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separator. *format* is a :c:func:`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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.. versionadded:: 2.4
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.. deprecated:: 2.7
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This function is removed in Python 2.7 and 3.1. Use :func:`PyOS_double_to_string`
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instead.
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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:type:`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:: 2.7
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.. c:function:: double PyOS_ascii_atof(const char *nptr)
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Convert a string to a :c:type:`double` in a locale-independent way.
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See the Unix man page :manpage:`atof(2)` for details.
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.. versionadded:: 2.4
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.. deprecated:: 3.1
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Use :c:func:`PyOS_string_to_double` instead.
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.. c:function:: 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 :c:func:`strcmp` except that it ignores the case.
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.. versionadded:: 2.6
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.. c:function:: 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 :c:func:`strncmp` except that it ignores the case.
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.. versionadded:: 2.6
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