strtoumax, _strtoumax_l, wcstoumax, _wcstoumax_l


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Converts strings to an integer value of the largest supported unsigned integer type.

uintmax_t strtoumax(  
   const char *nptr,  
   char **endptr,  
   int base   
uintmax_t _strtoumax_l(  
   const char *nptr,  
   char **endptr,  
   int base,  
   _locale_t locale  
uintmax_t wcstoumax(  
   const wchar_t *nptr,  
   wchar_t **endptr,  
   int base   
uintmax_t _wcstoumax_l(  
   const wchar_t *nptr,  
   wchar_t **endptr,  
   int base,  
   _locale_t locale  


Null-terminated string to convert.

Pointer to the character that stops the scan.

Number base to use.

Locale to use.

strtoumax returns the converted value, if any, or UINTMAX_MAX on overflow. strtoumax returns 0 if no conversion can be performed. wcstoumax returns values analogously to strtoumax. For both functions, errno is set to ERANGE if overflow or underflow occurs.

For more information about return codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Each of these functions converts the input string nptr to a uintmax_t integer value.

strtoumax stops reading the string nptr at the first character it cannot recognize as part of a number. This may be the terminating null character, or it may be the first numeric character that's greater than or equal to base. The LC_NUMERIC category setting of the locale determines the recognition of the radix character in nptr. For more information, see setlocale, _wsetlocale. strtoumax and wcstoumax use the current locale; _strtoumax_l and _wcstoumax_l are identical except that they instead use the locale that's passed in. For more information, see Locale.

If endptr is not NULL, a pointer to the character that stopped the scan is stored at the location that's pointed to by endptr. If no conversion can be performed (no valid digits were found or an invalid base was specified), the value of nptr is stored at the location that's pointed to by endptr.

The wide-character version of strtoumax is wcstoumax; its nptr argument is a wide-character string. Otherwise, these functions behave identically.

Generic-Text Routine Mappings

TCHAR.H routine_UNICODE & _MBCS not defined_MBCS defined_UNICODE defined

strtoumax expects nptr to point to a string of the following form:

[whitespace] [{+ | }] [0 [{ x | X }]] [digits | [letters]]

A whitespace may consist of space and tab characters, which are ignored; digits are one or more decimal digits; letters are one or more of the letters 'a' through 'z' (or 'A' through 'Z'). The first character that does not fit this form stops the scan. If base is between 2 and 36, then it is used as the base of the number. If base is 0, the initial characters of the string that's pointed to by nptr are used to determine the base. If the first character is '0' and the second character is not 'x' or 'X', the string is interpreted as an octal integer. If the first character is '0' and the second character is 'x' or 'X', the string is interpreted as a hexadecimal integer. If the first character is '1' through '9', the string is interpreted as a decimal integer. The letters 'a' through 'z' (or 'A' through 'Z') are assigned the values 10 through 35; only letters whose assigned values are less than base are permitted. The first character outside the range of the base stops the scan. For example, if base is 0 and the first character scanned is '0', an octal integer is assumed and an '8' or '9' character would stop the scan. strtoumax allows a plus sign (+) or minus sign () prefix; a leading minus sign indicates that the return value is the two’s complement of the absolute value of the converted string.

RoutineRequired header
wcstoumax<stdlib.h> or <wchar.h>
_wcstoumax_l<stdlib.h> or <wchar.h>

For additional compatibility information, see Compatibility.

See the example for strtod.


Data Conversion
setlocale, _wsetlocale
String to Numeric Value Functions
strtod, _strtod_l, wcstod, _wcstod_l
strtoimax, _strtoimax_l, wcstoimax, _wcstoimax_l
strtol, wcstol, _strtol_l, _wcstol_l
strtoul, _strtoul_l, wcstoul, _wcstoul_l
strtoll, _strtoll_l, wcstoll, _wcstoll_l
atof, _atof_l, _wtof, _wtof_l