3.6. strcat

char *strcat( char * restrict s1, const char * restrict s2);

strcat concatenates string s2 to end of string s1, and returns s1.

strcat can be written using strlen and strcpy:

        strcpy( &s1[strlen(s1)], s2);

Since strcat and strcpy return their first argument, the function return value can be used to simplify the writing of certain code.

For example, say we have a PC directory name and a file name, and we want to construct a complete path name:

        char dir[80] = "C:\\OSP\\A3";
        char fname[80] = "X.C";
        char path[80];

We want to set path to "C:\\OSP\\A3\\X.C" which requires copying the directory name, appending a backslash, then appending the filename:

        strcpy( path, dir);
        strcat( path, "\\");
        strcat( path, fname);

This can be done in one statement, using the strcpy and strcat return values as arguments to strcat:

        strcat( strcat( strcpy( path, dir), "\\"), fname);