pure C string

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string initialization

in pure C, string is a char array terminating with NULL(‘\0’). To initialize an array of char(string) is with a string literal(a double-quotaed string).

in general, the string literal is used as the initializer for an array of char; anywhere else, it is a static array of chars, which shouldn’t be modified by a pointer.

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/* initialize a string in C 
 * the size of s1 is taken from the size of the initializer
 */
	char s1[] = "hello world" ; 
// or 
	char s1[12] = "hello world"; 
/* common errors */
	char s2[];
	s2 = "hello world"
// error: storage size of 's2' isn't known 
	char s2[12];
	s2 = "hello world"
// error:  invalid array assignment 
/* there is no "=" operator defined for char array in C 
   using strcpy()
*/
``` 
## char pointer arithmetic 
```c
	char s1[12];
	*s1++ ;	
/* error:  lvalue requied as increment operand
 * s3 is an array, can't modify the address of an array. the difference between pointer and array 
*/ 
	 char* s2 = s1; 
	 *s2++;
/* s2 is a pointer to s1, ++ is ok */

string.h

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/* concatenate two strings */
strcat(char* s1, const char* s2) ;
strncat(char* s1, const char* s2, size_t n); 
/*  locate the first/last occurance of char c in string s */
strchr(const char* s1, int c);
memchr(const void* s1, int c, size_t n);
strrchr(const char* s1, int c); 
/*  compare s1 and s2 alphabetically */
strcmp(const char* s1, const char* s2);	
strncmp(const char* s1, const char* s2, size_t n);
memcmp(const void* s1, const void* s2, size_t n);
/*  copy s2 to s1 */
strcpy(char *s1, const char *s2); 
memcpy(void* s1, void* s2, size_t n);
/* number of bytes, not including terminating NULL; sizeof() will inlcude the terminating NULL */
strlen(const char* s1); 
/* find the first occurance of substring s2 in s1 */
strstr(const char *s1,  const char *s2);
/* split string s1 into a sequence of tokens by s2 */
strtok(char* s1, const char* s2);

\ is replaced by in C++.
and be aware of downs of C string.