Question

For example

sprintf(pos,"%f ",cl.snap.ps.origin[0]); //don't start with strcat
sprintf(tmp,"%f ",cl.snap.ps.origin[1]);strcat(pos, tmp);

fine.

with

sprintf(tmp,"%f ",cl.snap.ps.origin[0]);strcat(pos, tmp);
sprintf(tmp,"%f ",cl.snap.ps.origin[1]);strcat(pos, tmp);

not fine.

Answer 1

The strcat() function expects that the destination argument already contains a properly null-terminated string. In your case, it sounds like pos contains some junk that looks like a null-terminated string, but isn’t what you expect. strcat() is dutifully appending on to the end of that junk.

One way to fix this is to initialise pos before your code:

pos[0] = '\0';
sprintf(tmp,"%f ",cl.snap.ps.origin[0]);strcat(pos, tmp);
sprintf(tmp,"%f ",cl.snap.ps.origin[1]);strcat(pos, tmp);