Many people think that the difficulty in the C language is the pointer, and the understanding of the pointer is directly related to the programs, so, some of the source code of the standard functions that the C compiler usually have, they will read them. It can be understood by the pointers and strings.
1. Strlen (), calculate the string length
Int strlen (const char string) {INT i = 0; while (string [i]) i ; returni i;} 2. Strcpy (), string copy.
Char * STRCPY (CHAR * DESTINATION, Const Char * Source) {While (* Destinaton = * Source ); Return (Destination-1);}
3. STRCAT (), the connection of the string.
Char * strcat (char * target) {char * original = target; while (* target) Target ; // Find the end of the string while (* target = * source ); returnal);} 4. Streql () determines whether the two strings are equal.
INT streql (char * str1, char * str2) {while (* str1 == * str2) && (* str1)) {str1 ; str2 ;} return (* str1 == null) && (* str2 == null ));
5. Strchr () looks for a character in a string.
Char * strchr (const char * string, int letter) {while ((* string! = letter) & (* string)) String ; return (string);}
6. chrcnt (), calculates the number of times that appears in a string in a string.
INT chrcnt (const char * string, int letter) {int count = 0; while (* string) if (* string == letter) count ; return count;}
7. Strcmp (), determine if the two strings are equal.
INT strcmp (const char * str2) {while (* str1 == * str2) && (* str1)) {str1 ; str2 ;} if ((* str1 == * str2) && (! * Str1)) // Same strings Return O; ELSE IF ((* str1) && (! * str2)) // Same But str1 lonrge RETURN-1; ELSE IF ((* str2) && (! * str1)) //// SAME BUT STR2 LONGER ELSE RETURN ((* STR1> * STR2)? - 1: 1);}
