сцепление строк си

Есть две специальные функции:

char* strcat(char* dest, const char* source) // просто сцепление.
char* strncat(char* dest, const char* source, size_t size) // с указание сколько символов добавлять к первой строке

#include < string.h >
char *strcat(char * restrict s1,const char * restrict s2);

Description
The strcat function appends a copy of the string pointed to by s2 (including the
terminating null character) to the end of the string pointed to by s1. The initial character
of s2 overwrites the null character at the end of s1. If copying takes place between
objects that overlap, the behavior is unde?ned.
Returns
The strcat function returns the value of s1.
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