strspn
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <string.h> | ||
| size_t strspn( const char *dest, const char *src ); | ||
Returns the length of the maximum initial segment (span) of the null-terminated byte string pointed to by dest, that consists of only the characters 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 from the null-terminated byte string pointed to by src
Example
Run this code
#include <string.h> #include <stdio.h> int main(void) { const char *string = "abcde312$#@"; const char *low_alpha = "qwertyuiopasdfghjklzxcvbnm"; size_t spnsz = strspn(string, low_alpha); printf("After skipping initial lowercase letters from '%s'\n" "The remainder is '%s'\n", string, string+spnsz); }
Output:
After skipping initial lowercase letters from 'abcde312$#@' The remainder is '312$#@'
References
- C11 standard (ISO/IEC 9899:2011):
- 7.24.5.6 The strspn function (p: 369)
 
- C99 standard (ISO/IEC 9899:1999):
- 7.21.5.6 The strspn function (p: 332)
 
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.11.5.6 The strspn function
 
See also
| returns the length of the maximum initial segment that consists of only the characters not found in another byte string (function) | |
| (C95) | returns the length of the maximum initial segment that consists of only the wide characters found in another wide string (function) | 
| finds the first location of any character in one string, in another string (function) |