longjmp
| Defined in header <setjmp.h>
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| void longjmp( jmp_buf env, int status ); |
(until C11) | |
| _Noreturn void longjmp( jmp_buf env, int status ); |
(since C11) (until C23) |
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| [[noreturn]] void longjmp( jmp_buf env, int status ); |
(since C23) | |
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 (whether by return or by a different longjmp higher up the stack), the behavior is undefined. In other words, only long jumps up the call stack are allowed.
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Jumping across threads (if the function that called |
(since C11) |
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If when setjmp was called, a VLA or another variably-modified type variable was in scope and control left that scope, On the way up the stack, void g(int n) { int a[n]; // a may remain allocated h(n); // does not return } void h(int n) { int b[n]; // b may remain allocated longjmp(buf, 2); // might cause a memory leak for h's b and g's a } |
(since C99) |
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 intended for handling unexpected error conditions where the function cannot return meaningfully. This is similar to exception handling in other programming languages.
Example
#include <stdio.h> #include <setjmp.h> #include <stdnoreturn.h> jmp_buf my_jump_buffer; noreturn void foo(int status) { printf("foo(%d) called\n", status); longjmp(my_jump_buffer, status + 1); // will return status+1 out of setjmp } int main(void) { volatile int count = 0; // modified local vars in setjmp scope must be volatile if (setjmp(my_jump_buffer) != 5) // compare against constant in an if foo(++count); }
Output:
foo(1) called foo(2) called foo(3) called foo(4) called
References
- C17 standard (ISO/IEC 9899:2018):
- 7.13.2.1 The longjmp macro (p: 191-192)
- C11 standard (ISO/IEC 9899:2011):
- 7.13.2.1 The longjmp macro (p: 263-264)
- C99 standard (ISO/IEC 9899:1999):
- 7.13.2.1 The longjmp macro (p: 244-245)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.6.2.1 The longjmp function
See also
| saves the context (function macro) | |
| C++ documentation for longjmp
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