Setjmp Library

The Setjmp library contains functions and types definitions for bypassing the normal function call and return discipline.

jmp_buf is an array of unsigned int type suitable for holding information needed to restore a calling environment. Type declaration is contained in the sejmp.h header file which can be found in the include folder of the compiler.

Setjmp

Prototype	int Setjmp(jmp_buf env);
Description	This function saves calling position for a later use by Longjmp.
Parameters	`env:` buffer suitable for holding information needed for restoring calling environment
Returns	`0` if the return is from direct invocation `nonzero value` if the return is from a call to `Longjmp` (this value will be set by the `Longjmp` routine)
Requires	Nothing.
Example	jmp_buf buf; ... Setjmp(buf);
Notes	None.

Longjmp

Prototype	void Longjmp(jmp_buf env, int val);
Description	Restores calling environment saved in `env` buffer by the most recent invocation of `Setjmp`. If there has been no such invocation, or the function containing the invocation of Setjmp has terminated in the interim, the behavior is undefined.
Parameters	`env:` buffer holding the information saved by the corresponding `Setjmp` invocation `val:` value to be returned by the corresponding `Setjmp` function
Returns	Nothing.
Requires	Invocation of `Longjmp` must occur before return from the function in which `Setjmp` was called encounters.
Example	jmp_buf buf; ... Longjmp(buf, 2);
Notes	None.

Library Example

This example demonstrates function cross calling using the Setjmp and Longjmp functions. When called, Setjmp saves its calling environment in its jmp_buf argument for a later use by Longjmp. Longjmp, on the other hand, restores the environment saved by the most recent invocation of Setjmp with the corresponding jmp_buf argument.

Copy Code To Clipboard

#include <Setjmp.h>

jmp_buf buf;             // Note: Program flow diagrams are indexed according
                         //       to the sequence of execution

void func33(){           //  2<------------|
                         //                |
  Delay_ms(1000);        //                |
                         //                |
  asm nop;               //                |
  Longjmp(buf, 2);       //  3---------------->|
  asm nop;               //                |   |
                         //                |   |
}                        //                |   |
                         //                |   |
void func(){             //  1<--------|   |   |
                         //            |   |   |
  portb = 3;             //            |   |   |
  if (Setjmp(buf) == 2)  //  3<----------------|
    portb = 1;           //  4-->|     |   |
  else                   //      |     |   |
    func33();            //  2------------>|
                         //      |     |
                         //  4<--|     |
}                        //  5----->|  |
                         //         |  |
void main() {            //         |  |
                         //         |  |
  PORTB = 0;             //         |  |
  TRISB = 0;             //         |  |
                         //         |  |
  asm nop;               //         |  |
                         //         |  |
  func();                //  1-------->|
                         //         |
  asm nop;               //  5<-----|
  Delay_ms(1000);
  PORTB = 0xFFFF;
}

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