Can the input and output strings to sprintf() be the same?

Question

I have used this type of convention many times in my code in the past:

strcpy ( cTmpA, \"hello\" );
sprintf ( cTmpA, \"%s world\", cTmpA );

Answer 1

While it is valid K&R C, you probably want to rather know if it's valid POSIX - see sprintf Specification. We read:

If copying takes place between objects that overlap as a result of a call to sprintf() or snprintf(), the results are undefined.