<string.h> provides null-terminated string functions (strlen, strcpy, strcat, strcmp) and memory operations (memcpy, memmove, memset). Avoid strcpy/strcat (unsafe); use bounded variants or snprintf instead.

The mem* functions work on raw bytes; the str* functions assume null termination.

This example tokenizes a CSV line using strtok and measures each field.

// compile: gcc -o stringexample stringexample.c
// run: ./stringexample
// description: tokenize CSV line by comma and print each field
 
#include <string.h>
#include <stdio.h>
 
int main() {
    char line[] = "alice,30,engineer,london";
    char* tok = strtok(line, ",");
    int field = 0;
 
    while (tok) {
        printf("field %d: \"%s\" (len %zu)\n", field++, tok, strlen(tok));
        tok = strtok(NULL, ",");
    }
 
    return 0;
}

String length:

• strlen(str): length (bytes until null terminator)

String copying (null-terminated):

• strcpy(dst, src): copy string (unsafe: no bounds check, use strncpy)
• strncpy(dst, src, n): copy up to n characters (pads with nulls if n > length)
• strdup(src): allocate and copy string (POSIX, not standard C)
• strndup(src, n): allocate and copy up to n characters (POSIX)

String concatenation (null-terminated):

• strcat(dst, src): append string (unsafe, use strncat)
• strncat(dst, src, n): append up to n characters

String comparison (null-terminated):

• strcmp(s1, s2): compare lexicographically (returns <0, 0, or >0)
• strncmp(s1, s2, n): compare first n characters
• strcasecmp(s1, s2): case-insensitive compare (POSIX)
• strncasecmp(s1, s2, n): case-insensitive compare first n (POSIX)

String searching (null-terminated):

• strchr(str, ch): find first occurrence of char (returns pointer or NULL)
• strrchr(str, ch): find last occurrence
• strstr(haystack, needle): find substring
• strcspn(str, reject): length of prefix not containing any reject chars
• strspn(str, accept): length of prefix containing only accept chars
• strpbrk(str, accept): find first char in accept set

String splitting:

• strtok(str, delim): extract token separated by delim chars (not reentrant)
• strtok_r(str, delim, &ptr): reentrant version (POSIX)

Memory operations (byte-level, works on any data):

• memcpy(dst, src, n): copy n bytes (undefined if regions overlap)
• memmove(dst, src, n): copy n bytes (safe with overlap)
• memset(dst, byte, n): fill n bytes with byte value
• memcmp(s1, s2, n): compare n bytes
• memchr(ptr, byte, n): find first occurrence of byte
• memccpy(dst, src, byte, n): copy until byte found (POSIX)