strcspn

 

C

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

Algorithms

Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (C11)

Technical Specifications

Symbol index

 

Strings library

Byte strings

Multibyte strings

Wide strings

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to and from numeric formats
atoiatolatoll (C99) atof strtolstrtoll (C99) strtoulstrtoull (C99)	strtoimaxstrtoumax (C99)(C99) strtofstrtodstrtold (C99)(C99) strfromfstrfromdstrfromld (C23)(C23)(C23)
String manipulation
strcpystrcpy_s (C11) strncpystrncpy_s (C11) strcatstrcat_s (C11)	strncatstrncat_s (C11) strxfrm strdup (C23) strndup (C23)
String examination
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
Memory manipulation
memchr memcmp memsetmemset_explicitmemset_s (C23)(C11)	memcpymemcpy_s (C11) memmovememmove_s (C11) memccpy (C23)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (C11)(C11)

 

Defined in header <string.h>
size_t strcspn( const char *dest, const char *src );

Returns the length of the maximum initial segment of the null-terminated byte string pointed to by dest, that consists of only the characters not found in the null-terminated byte string pointed to by src.

The behavior is undefined if either dest or src is not a pointer to a null-terminated byte string.

Parameters

dest	-	pointer to the null-terminated byte string to be analyzed
src	-	pointer to the null-terminated byte string that contains the characters to search for

Return value

The length of the maximum initial segment that contains only characters not found in the null-terminated byte string pointed to by src

Notes

The function name stands for "complementary span" because the function searches for characters not found in src, that is the complement of src.

Example

Run this code

#include <string.h>
#include <stdio.h>
 
int main(void)
{
    const char *string = "abcde312$#@";
    const char *invalid = "*$#";
 
    size_t valid_len = strcspn(string, invalid);
    if(valid_len != strlen(string))
       printf("'%s' contains invalid chars starting at position %zu\n",
               string, valid_len);
}

Output:

'abcde312$#@' contains invalid chars starting at position 8

References

• C11 standard (ISO/IEC 9899:2011):

• 7.24.5.3 The strcspn function (p: 368)

• C99 standard (ISO/IEC 9899:1999):

• 7.21.5.3 The strcspn function (p: 331)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.11.5.3 The strcspn function

See also

strspn	returns the length of the maximum initial segment that consists of only the characters found in another byte string (function)
wcscspn (C95)	returns the length of the maximum initial segment that consists of only the wide chars not found in another wide string (function)
strpbrk	finds the first location of any character in one string, in another string (function)
C++ documentation for strcspn