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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:

- the entire controlling expression of if, switch, while, do-while, for

    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)) { ...

- the entire expression of an expression statement (possibly cast to `void`).

    setjmp(env);

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

Upon return to the scope of `setjmp`, all accessible objects, floating-point status flags, and other components of the abstract machine 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 if they have been changed since the setjmp invocation.

### [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

Run this code

    #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; // modified locals in setjmp scope 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(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

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

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