NAME¶

std::longjmp - std::longjmp

Synopsis¶

Defined in header <csetjmp>
void longjmp( std::jmp_buf env, int status ); (until C++17)
[[noreturn]] void longjmp( std::jmp_buf env, int status ); (since C++17)

Loads the execution context env saved by a previous call to setjmp. This function
does not return. Control is transferred to the call site of the macro setjmp that
set up env. That setjmp then returns the value, passed as the status.

If the function that called setjmp has exited, the behavior is undefined (in other
words, only long jumps up the call stack are allowed)

No destructors for automatic objects are called. If replacing of std::longjmp with
throw and setjmp with catch would execute a non-trivial destructor for any automatic
object, the behavior of such std::longjmp is undefined.

Parameters¶

env - variable referring to the execution state of the program saved by setjmp
status - the value to return from setjmp. If it is equal to 0, 1 is used
instead

Return value¶

(none)

Notes¶

longjmp is the mechanism used in C to handle unexpected error conditions where the
function cannot return meaningfully. C++ generally uses exception handling for this
purpose.

Example¶

// Run this code

#include <iostream>
#include <csetjmp>

std::jmp_buf my_jump_buffer;

[[noreturn]] void foo(int count)
{
std::cout << "foo(" << count << ") called\n";
std::longjmp(my_jump_buffer, count+1); // setjmp() will return count+1
}

int main()
{
volatile int count = 0; // modified locals in setjmp scope must be volatile
if (setjmp(my_jump_buffer) != 5) { // equality against constant expression in an if
count = count + 1; // ++count, count += 1, etc on 'volatile'-qualified
// left operand are deprecated since C++20 (P1152)
foo(count); // This will cause setjmp() to exit
}
}

Output:¶

foo(1) called
foo(2) called
foo(3) called
foo(4) called

See also¶

setjmp saves the context
(function macro)