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.
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 |
(none).
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.
#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); // setjmp() will return count+1 } int main() { volatile int count = 0; // local variables must be volatile for setjmp if (setjmp(jump_buffer) != 9) { 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
saves the context (function macro) |
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