Help on setjmp & longjmp for strings

[Andr3w]

Hi,

I'd like to know if there is a way to implement setjmp & longjmp to recover from the following scenario:

// allocate buffer
char *m = malloc(10);
 
// get buffer
gets_s(m , sizeof(m));
 

Now if the user types more than 10 chars we have a segmentation error but when I do the following it doesn't find it:

// define our error handler
        void static __cdecl pStrHandler( int pSig );
 
    // dummy var to save the env
    jmp_buf env_b;
 
    // entry point for our application
    int main( int argc, char **argv)
    {
        // declare more vars
        // ..
        //
        int marker; // marker for env jump
        char b[10]; // buffer to raise exception
 
        typedef void (*ptrTSigHndlr)(int);
 
        // set up a pointer to the OldHandler in order to replace it
        ptrTSigHndlr OldHanlder;
 
        // let’s check if the signal handler is allocated ok
        if ( (OldHandler = signal ( SIGSEGV, pStrHandler ) )  )
        {
            // failed to set up signal hanlder, abort
            abort();
        }
 
        // save the environment for recovery to env_b buf
        marker = set_jmp(env_b);
 
        // try the potential error code
        if ( marker == 0 )
        {
 
            gets_s(b, sizeof(b)); // now input as many chars as you want
        }
        else {  // do stuff you want, maybe a lookup error code function? 
}
 
 
return 0;    
}
 
//define our handler…
void static __cdecl pStrHandler( int pSig )
{
  // error handling code here 
}
 

Can you help me solve this? I works fine for 1 byte char but I want for char arrays...

Any help is great :)

[weaknessforcats]

I think gets_s is a Microsoft whiz-bang. That being the case I think you need to call _set_invalid_parameter_handler.

I don't think there's a long jump in your scenario.

[Andr3w]

Well this gives me errors even if i use gets, I thought about going for

if( gets(a /* buff */) == NULL)
{
   // do stuff
}
 

but this doesn't work..in VS6 is leaves the leak go on (and only if you use the value gets an error) but in VS8 at least the debbuger informs you of the assertion error. While in visual studio 8 I can use the _set_invalid_parameter_hanlder() and _invalid_parameter_hanlder I can't in Visual Studio 6. So I have to go with gets and setjmp/longjmp, fine by me but setjmp and longjmp don't work (the above code is sufficient to illustrate my problem if you change the gets_s to gets and increase the buffer to a value larger than 1)

Please help a bit ;)

[weaknessforcats]

// allocate buffer
char *m = malloc(10);

// get buffer
gets_s(m , sizeof(m));

While we are chatting along I just noticed your original code above.

You are aware that sizeof(m) is always 4 ?? That is, it's the size of the address.

[weaknessforcats]

I never did understand why you are using VC++ 6.0. Even with all the service packs, it doesn't work. There are bugs in the templates, partial specializtion is not supported not is covariance, etc.

The current release is 8.0 and 9.0 is almost here.

As to get_s(), it is designed to validate the buffer size and gag if it is too small. That assumes you know the correct buffer size at the outset. If you do not, then I suggest you implement a function that will accept up to, say 10, characters and if there is no end-of-line or end-of file condition, that it packs away the first 10 and accepts another 10. That way it can keep packing away groups of 10 unitl it sees and end-of-line or end-of-file.

This way you know the buffer size and you realloc as necessary until the inout is processed.

What do you think?

[Andr3w]

Actually I am not using VS6 I am using VS9 (beta) but I am asking for compatibility for VS6 because they have it on my uni and they want their c files to be run on VS6.. I know it's hell crappy it's like 10 years old... Well that's why I am doing all this fuzz, _set_invalid_parameter() works neat and I used it before I posted here. The thing is I wanted to get the job done using setjmp and longjmp. Also in my code above I have actually done that mistake... :P

[weaknessforcats]

You are mentioning they. As in users that have VS6 and are using your code??

Maybe you should build a library using VS9 and give them the library and a header file. They can merrily go using VC6 and linking with your library.