What is the difference between setjmp() and longjmp() in c++ i am confused

Question

What is the difference between setjmp() and longjmp() in c++ i am confused

Answer 1

One (setjmp()) sets the bookmark, other (longjmp()) jumps to it.

Answer 2

Don't use setjmp/longjmp in C++. The problem is that setjmp/longjmp is a low level C API that does not properly handle stack unwinding. So, if you had code like this:

void dont_do_this(jmp_buf jmp)
{
    std::string leakme("bad");
    longjmp(jmp, leakme.length());
}

the string destructor will not be called and you'll leak memory.

It's possible even worse things can happen as this is undefined behavior. According to section 18.7/4:

The function signature longjmp(jmp_buf jbuf, int val) has more restricted behavior in this International Standard. If any automatic objects would be destroyed by a thrown exception transferring control to another (destination) point in the program, then a call to longjmp(jbuf, val) at the throw point that transfers control to the same (destination) point has undefined behavior.

Answer 3

Treat longjump as a non local goto. You set a point to jump back using setjump and jump back to it using longjmp. Read the following two links to understand it better

http://www.cppreference.com/wiki/c/other/setjmp

Also read about the longjmp to understand the usage.