Difference between revisions of "cpp/utility/program/longjmp"
(address UB in this example too) |
m (usage note) |
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If the function that called {{lc|setjmp}} has exited, the behavior is undefined (in other words, only long jumps up the call stack are allowed) | If the function that called {{lc|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 {{tt|std::longjmp}} with {{c|throw}} and {{lc|setjmp}} with {{c|catch}} would execute a non-trivial destructor for any automatic object, the behavior of such {{ | + | No destructors for automatic objects are called. If replacing of {{tt|std::longjmp}} with {{c|throw}} and {{lc|setjmp}} with {{c|catch}} would execute a non-trivial destructor for any automatic object, the behavior of such {{tt|std::longjmp}} is undefined. |
===Parameters=== | ===Parameters=== | ||
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===Return value=== | ===Return value=== | ||
(none) | (none) | ||
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| + | ===Notes=== | ||
| + | {{tt|longjmp}} is the mechanism used in C to handle unexpected error conditions where the function cannot return meaningfully. C++ generally uses [[cpp/language/exceptions|exception handling]] for this purpose. | ||
===Example=== | ===Example=== | ||
Revision as of 15:25, 2 December 2014
| Defined in header <csetjmp>
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| void longjmp( std::jmp_buf env, int status ); |
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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.
Contents |
Parameters
| env | - | variable referring to the execution state of the program saved by std::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
#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; // 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
See also
| saves the context (function macro) | |
| C documentation for longjmp
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