# string.h Functions — C Programming

Source: https://www.geekswithgeeks.com/en/c/c-string-functions

> Standard helpers for length, copy, compare and concatenation.

## strlen & strcpy

`strlen` counts characters before `'\0'` (excluding it). `strcpy` copies a string including its null terminator.

```c
#include <string.h>
#include <stdio.h>

char src[] = "hello";
char dest[10];

printf("%zu\n", strlen(src)); // 5
strcpy(dest, src);
printf("%s\n", dest);
```

Output:

```
5
hello
```

## strcmp & strcat

`strcmp` returns `0` when strings are equal (never use `==` to compare strings!). `strcat` appends one string to another.

```c
char a[20] = "cat";
char b[]   = "cat";

if (strcmp(a, b) == 0) {
    printf("equal\n");
}

strcat(a, "fish");
printf("%s\n", a);
```

Output:

```
equal
catfish
```

## Buffer must be big enough

`strcpy`/`strcat` don't check the destination's size — writing past it corrupts memory. Prefer `strncpy`/`strncat` with an explicit size limit.

**Quiz:** Why should you avoid `if (str1 == str2)` to compare two C strings?

- [x] It compares pointer addresses, not contents
- [ ] It always returns true
- [ ] It only works with numbers

*Answer:* It compares pointer addresses, not contents. Arrays decay to pointers, so `==` compares addresses; use `strcmp` for content.