1 .. highlightlang:: c 2 3 .. _string-conversion: 4 5 String conversion and formatting 6 ================================ 7 8 Functions for number conversion and formatted string output. 9 10 11 .. c:function:: int PyOS_snprintf(char *str, size_t size, const char *format, ...) 12 13 Output not more than *size* bytes to *str* according to the format string 14 *format* and the extra arguments. See the Unix man page :manpage:`snprintf(2)`. 15 16 17 .. c:function:: int PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va) 18 19 Output not more than *size* bytes to *str* according to the format string 20 *format* and the variable argument list *va*. Unix man page 21 :manpage:`vsnprintf(2)`. 22 23 :c:func:`PyOS_snprintf` and :c:func:`PyOS_vsnprintf` wrap the Standard C library 24 functions :c:func:`snprintf` and :c:func:`vsnprintf`. Their purpose is to 25 guarantee consistent behavior in corner cases, which the Standard C functions do 26 not. 27 28 The wrappers ensure that *str*[*size*-1] is always ``'\0'`` upon return. They 29 never write more than *size* bytes (including the trailing ``'\0'`` into str. 30 Both functions require that ``str != NULL``, ``size > 0`` and ``format != 31 NULL``. 32 33 If the platform doesn't have :c:func:`vsnprintf` and the buffer size needed to 34 avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a 35 *Py_FatalError*. 36 37 The return value (*rv*) for these functions should be interpreted as follows: 38 39 * When ``0 <= rv < size``, the output conversion was successful and *rv* 40 characters were written to *str* (excluding the trailing ``'\0'`` byte at 41 *str*[*rv*]). 42 43 * When ``rv >= size``, the output conversion was truncated and a buffer with 44 ``rv + 1`` bytes would have been needed to succeed. *str*[*size*-1] is ``'\0'`` 45 in this case. 46 47 * When ``rv < 0``, "something bad happened." *str*[*size*-1] is ``'\0'`` in 48 this case too, but the rest of *str* is undefined. The exact cause of the error 49 depends on the underlying platform. 50 51 The following functions provide locale-independent string to number conversions. 52 53 54 .. c:function:: double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception) 55 56 Convert a string ``s`` to a :c:type:`double`, raising a Python 57 exception on failure. The set of accepted strings corresponds to 58 the set of strings accepted by Python's :func:`float` constructor, 59 except that ``s`` must not have leading or trailing whitespace. 60 The conversion is independent of the current locale. 61 62 If ``endptr`` is ``NULL``, convert the whole string. Raise 63 ValueError and return ``-1.0`` if the string is not a valid 64 representation of a floating-point number. 65 66 If endptr is not ``NULL``, convert as much of the string as 67 possible and set ``*endptr`` to point to the first unconverted 68 character. If no initial segment of the string is the valid 69 representation of a floating-point number, set ``*endptr`` to point 70 to the beginning of the string, raise ValueError, and return 71 ``-1.0``. 72 73 If ``s`` represents a value that is too large to store in a float 74 (for example, ``"1e500"`` is such a string on many platforms) then 75 if ``overflow_exception`` is ``NULL`` return ``Py_HUGE_VAL`` (with 76 an appropriate sign) and don't set any exception. Otherwise, 77 ``overflow_exception`` must point to a Python exception object; 78 raise that exception and return ``-1.0``. In both cases, set 79 ``*endptr`` to point to the first character after the converted value. 80 81 If any other error occurs during the conversion (for example an 82 out-of-memory error), set the appropriate Python exception and 83 return ``-1.0``. 84 85 .. versionadded:: 2.7 86 87 88 .. c:function:: double PyOS_ascii_strtod(const char *nptr, char **endptr) 89 90 Convert a string to a :c:type:`double`. This function behaves like the Standard C 91 function :c:func:`strtod` does in the C locale. It does this without changing the 92 current locale, since that would not be thread-safe. 93 94 :c:func:`PyOS_ascii_strtod` should typically be used for reading configuration 95 files or other non-user input that should be locale independent. 96 97 See the Unix man page :manpage:`strtod(2)` for details. 98 99 .. versionadded:: 2.4 100 101 .. deprecated:: 2.7 102 Use :c:func:`PyOS_string_to_double` instead. 103 104 105 106 .. c:function:: char* PyOS_ascii_formatd(char *buffer, size_t buf_len, const char *format, double d) 107 108 Convert a :c:type:`double` to a string using the ``'.'`` as the decimal 109 separator. *format* is a :c:func:`printf`\ -style format string specifying the 110 number format. Allowed conversion characters are ``'e'``, ``'E'``, ``'f'``, 111 ``'F'``, ``'g'`` and ``'G'``. 112 113 The return value is a pointer to *buffer* with the converted string or NULL if 114 the conversion failed. 115 116 .. versionadded:: 2.4 117 .. deprecated:: 2.7 118 This function is removed in Python 2.7 and 3.1. Use :func:`PyOS_double_to_string` 119 instead. 120 121 122 .. c:function:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype) 123 124 Convert a :c:type:`double` *val* to a string using supplied 125 *format_code*, *precision*, and *flags*. 126 127 *format_code* must be one of ``'e'``, ``'E'``, ``'f'``, ``'F'``, 128 ``'g'``, ``'G'`` or ``'r'``. For ``'r'``, the supplied *precision* 129 must be ``0`` and is ignored. The ``'r'`` format code specifies the 130 standard :func:`repr` format. 131 132 *flags* can be zero or more of the values *Py_DTSF_SIGN*, 133 *Py_DTSF_ADD_DOT_0*, or *Py_DTSF_ALT*, or-ed together: 134 135 * *Py_DTSF_SIGN* means to always precede the returned string with a sign 136 character, even if *val* is non-negative. 137 138 * *Py_DTSF_ADD_DOT_0* means to ensure that the returned string will not look 139 like an integer. 140 141 * *Py_DTSF_ALT* means to apply "alternate" formatting rules. See the 142 documentation for the :c:func:`PyOS_snprintf` ``'#'`` specifier for 143 details. 144 145 If *ptype* is non-NULL, then the value it points to will be set to one of 146 *Py_DTST_FINITE*, *Py_DTST_INFINITE*, or *Py_DTST_NAN*, signifying that 147 *val* is a finite number, an infinite number, or not a number, respectively. 148 149 The return value is a pointer to *buffer* with the converted string or 150 *NULL* if the conversion failed. The caller is responsible for freeing the 151 returned string by calling :c:func:`PyMem_Free`. 152 153 .. versionadded:: 2.7 154 155 156 .. c:function:: double PyOS_ascii_atof(const char *nptr) 157 158 Convert a string to a :c:type:`double` in a locale-independent way. 159 160 See the Unix man page :manpage:`atof(2)` for details. 161 162 .. versionadded:: 2.4 163 164 .. deprecated:: 3.1 165 Use :c:func:`PyOS_string_to_double` instead. 166 167 168 .. c:function:: char* PyOS_stricmp(char *s1, char *s2) 169 170 Case insensitive comparison of strings. The function works almost 171 identically to :c:func:`strcmp` except that it ignores the case. 172 173 .. versionadded:: 2.6 174 175 176 .. c:function:: char* PyOS_strnicmp(char *s1, char *s2, Py_ssize_t size) 177 178 Case insensitive comparison of strings. The function works almost 179 identically to :c:func:`strncmp` except that it ignores the case. 180 181 .. versionadded:: 2.6 182
