# <string.h>

**[<string.h>](https://en.cppreference.com/w/c/header/string)** 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.

## Example

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

```c
// 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;
}
```

## Common functions

**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)