In C, strncat() adds at most n characters from the source onto the end of the destination. It always writes an extra '\0' after those characters.
You pass the destination, the source, and the count. All three are required. The destination needs room for the old text, the new characters, and that extra '\0'. Include <string.h>.
Pass destination, source, and count. Start with this call.
strncat(dest, "world", 5);| Call | What it does |
|---|---|
strncat(dest, "world", 5) | Adds up to 5 characters from world, then writes '\0'. |
Include <string.h>. n is not the size of dest. Leave room for the final '\0'.
char *strncat(char *dest, const char *src, size_t n);| Parameter | Description |
|---|---|
| dest | Required. The C-string you add onto. It must have free space. |
| source | Required. The characters you copy from. |
| count | Required. The most characters to take from source. |
| Return Value | Description |
|---|---|
| dest pointer | The same destination pointer you passed in. |
n CharactersAppend only the first three letters of the source onto dest.
#include <stdio.h>
#include <string.h>
int main(void) {
char dest[16] = "Hi";
strncat(dest, "There", 3);
printf("%s\n", dest);
return 0;
}dest already has a terminator.T, h, e are appended.strncat always writes the terminator.HiThe.Use sizeof(dest) - strlen(dest) - 1 so the append cannot overflow the array.
#include <stdio.h>
#include <string.h>
int main(void) {
char dest[8] = "Hi";
size_t room = sizeof dest - strlen(dest) - 1;
strncat(dest, "ABCDEF", room);
printf("%s\n", dest);
return 0;
}"Hi" uses 2 + terminator → 5 free character slots."ABCDEF" are appended."HiABCDE" plus '\0' fills the buffer safely.n must reflect free space—strncat will not check sizeof for you.n Exceeds srcIf n is larger than the source length, the whole source is appended (still with a final '\0').
#include <stdio.h>
#include <string.h>
int main(void) {
char dest[16] = "Go";
strncat(dest, "!", 10);
printf("%s\n", dest);
return 0;
}"!" has length 1.'\0', so only '!' is copied."Go!".n does not create room—the buffer must already be big enough.Compare at most n characters of two C-strings.
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