strcpy and strcat cause problems sometimes

Question

hello I have a code like the one below

char *str ;

        strcpy(str, \"\\t<\");
        strcat(str, time);
        strcat(str, \">[\");
        strcat(s         


        

Answer 1

You don't allocate memory and you leave str uninitialized. All later writes are done through an uninitialized pointer that points "somewhere" - that's undefined behavior.

You have to allocate (and later free) memory large enough to hold the resulting string:

char *str = malloc( computeResultSizeSomehow() );
if( str == 0 ) {
   // malloc failed - handle as fatal error
}

//proceed with your code, then

free( str );