Question

I had an inverview today, and was asked to write a function of two strings concatenation. But after I’ve finished, I’ve heard, that generally the code is ok, but I’ve done a little error there. Checked it at home, but everything is working. Whats the problem?

char * strconcat (char *S1, char *S2){
    char *S3 = new char [strlen(S1) + strlen(S2) +1];
    strcpy(S3, S1);
    strcat(S3, S2);
    return S3;   
} 

Answer 1

char * strconcat (char *S1, char *S2){
    if(S1 == NULL || S2 == NULL)
         return NULL;
    int S1_len = strlen(S1);
    int S2_len = strlen(S2);
    char *S3 = new char [S1_len + S2_len +1];
    memset(S3, 0, S1_len + S2_len +1);
    strcpy(S3, S1);
    strcat(S3, S2);  // or memcpy(S3+S1_len, S2, S2_len);
    return S3;   
}