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setjmp

From cppreference.com
< cpp‎ | utility‎ | program
Defined in header <csetjmp>
#define setjmp(env) /* implementation-defined */

Saves the current execution context into a variable env of type std::jmp_buf. This variable can later be used to restore the current execution context by std::longjmp function. That is, when a call to std::longjmp function is made, the execution continues at the particular call site that constructed the std::jmp_buf variable passed to std::longjmp. In that case setjmp returns the value passed to std::longjmp.

The invocation of setjmp must appear only in one of the following contexts:

switch(setjmp(env)) { ..
  • one operand of a relational or equality operator with the other operand an integer constant expression, with the resulting expression being the entire controlling expression if, switch, while, do-while, for.
if(setjmp(env) > 0) { ...
  • the operand of a unary ! operator with the resulting expression being the entire controlling expression of if, switch, while, do-while, for.
while(!setjmp(env)) { ...
setjmp(env);

If setjmp appears in any other context, the behavior is undefined.

Upon return to the scope of setjmp, all accessible objects have the same values as they had when std::longjmp was executed, except for the non-volatile local variables in setjmp's scope, whose values are indeterminate.

Contents

[edit] Parameters

env - variable to save the execution state of the program to.

[edit] Return value

0 if the macro was called by the original code and the execution context was saved to env.

Non-zero value if a non-local jump was just performed. The return value is the same as passed to std::longjmp.

[edit] Example

#include <iostream>
#include <csetjmp>
 
std::jmp_buf jump_buffer;
 
[[noreturn]] void a(int count) 
{
    std::cout << "a(" << count << ") called\n";
    std::longjmp(jump_buffer, count+1);  // setjump() will return count+1
}
 
int main()
{
    volatile int count = 0; // locals in scope where longjmp returns must be volatile
    if (setjmp(jump_buffer) != 9) { // equality against constant expression in an if
        a(count++);  // This will cause setjmp() to exit
    }
}

Output:

a(0) called
a(1) called
a(2) called
a(3) called
a(4) called
a(5) called
a(6) called
a(7) called
a(8) called

[edit] See also

jumps to specified location
(function) [edit]
C documentation for setjmp