A goto statement implements a local jump of program execution, and
the longjmp() and setjmp() functions implement a nonlocal, or far,
jump of program execution.
Generally, a jump in execution of any kind should be avoided because
it is not considered good programming practice to use such statements
as goto and longjmp in your program.
A goto statement simply bypasses code in your program and jumps to
a predefined position. To use the goto statement, you give it a labeled
position to jump to. This predefined position must be within the same
function. You cannot implement gotos between functions.
When your program calls setjmp(), the current state of your program is
saved in a structure of type jmp_buf. Later, your program can call the
longjmp() function to restore the programís state as it was when you
called setjmp().Unlike the goto statement, the longjmp() and setjmp()
functions do not need to be implemented in the same function.
However, there is a major drawback to using these functions: your
program, when restored to its previously saved state, will lose its
references to any dynamically allocated memory between the
longjmp() and the setjmp(). This means you will waste memory for
every malloc() or calloc() you have implemented between your
longjmp() and setjmp(), and your program will be horribly inefficient.
It is highly recommended that you avoid using functions such as
longjmp() and setjmp() because they, like the goto statement, are
quite often an indication of poor programming practice.