Strcat

strcat is a function in the C standard library that appends a copy of the null-terminated string src to the end of the null-terminated string dest. The destination buffer must be large enough to hold the combined result plus the terminating null character. The function returns a pointer to dest.

Signature: char *strcat(char *dest, const char *src); It is declared in the header string.h.

Operation: strcat first locates the terminating null character of dest, then copies the characters from src to that position, including the terminating null. After the call, dest contains the concatenation of the two strings.

Important caveats: The function does not perform any bounds checking. If dest does not have enough space, this can cause buffer overflow, potentially crashing the program or introducing security vulnerabilities. It also assumes neither pointer is NULL and that src is a valid null-terminated string. If the memory regions pointed to by src and dest overlap, the behavior is undefined.

Safer alternatives: strncat appends at most a specified number of characters from src and still requires that dest have enough space for the result plus a terminating null. Misuse can still overflow if not carefully sized. strlcat (available on some systems) takes the full size of the destination buffer and performs overflow-aware concatenation, but it is not part of the C standard. In modern C++, std::string and its operators provide safer and more convenient string concatenation.

Example: char buf[20] = "hello"; strcat(buf, " world"); // buf now contains "hello world".