assertion

[MPrestonf12]

Im getting the error "debug assertion failed" I looked it up in the help file but it doesn't really explain it. anyway does anyone know what the cause of it is? thanks

[Technocrat]

Where are you getting it?
Assert comes up when something that should be true turn out to be false. Example:

ASSERT(a != NULL);
ASSERT(b != NULL);
c = a + b; 

You would get an assert if a or b = null

[parksie]

Not sure what that macro is, but there's a function called assert() that complains loudly when something's wrong.

[Zaei]

i think "assert" is a macro too. Otherwise, when you build in Release mode, you would get a speed hit from parameter passing, even if nothing took place, if you had a lot of asserts all over.

Ah, here it is:

in debug mode...
#define assert(exp) (void)( (exp) || (_assert(#exp, __FILE__, __LINE__), 0) )

and in release:
#define assert(exp)     ((void)0)

Z.

[Vlatko]

assert() is a macro too.
Here is one way of defining it yourself:

#define DEBUG
     #include <iostream.h>

     #ifndef DEBUG
        #define ASSERT(x)
   #else
       #define ASSERT(x) \
                if (! (x)) \                { \
                   cout << "ERROR!! Assert " << #x << " failed\n"; \
                   cout << " on line " << __LINE__  << "\n"; \
                 cout << " in file " << __FILE__ << "\n";  \
               }
   #endif 

  int main()
    {
       int x = 5;
       cout << "First assert: \n";
       ASSERT(x==5);
       cout << "\nSecond assert: \n";
       ASSERT(x != 5);
       cout << "\nDone.\n";
     return 0;
 } 

Output: First assert:

Second assert:
ERROR!! Assert x !=5 failed
on line 24
in file test1704.cpp
Done.

[parksie]

You forgot your line-continuation characters in the definition of ASSERT. Oh, and use <iostream> instead

[Vlatko]

The line-continuation characters were there but they are gone now. It is something with the php tags.

[parksie]

Hmmm...that's okay then

Er, John?

[Zaei]

#define Assert(a, b) assert(a && b)

INT main()
{
   INT x = 2;
   Assert(x != 2, "X == 2 in INT main()");
}

Game Programming Gems has a section on writing custom assert macros, with stuff like an "Ignore Always" option, and the one I just typed. Great stuff.

Z.

[dubae524]

I got an assertion error when the program (I guess, because it said the problem was with fseek.c,) was trying to use fseek! Look!

#include <fstream.h>
#include <stdlib.h>
#include <iostream.h>
#include <stdio.h>

void main(void) {
FILE *testafile;
char myfilechar;
testafile = fopen("D:\testfile.fil", "r");
myfilechar = (char) fseek(testafile, 4, 0);
fclose(testafile);
printf("%c", myfilechar);
}

What is up with this! What in the #$%#$%#$ is assertion doing there in the first place! It is so ridiculous!

Anyway, enough of my ranting and raving about this sometimes BS-ing language--it's the only one out there close to decent. But can somebody help me out with and/or explain to me this problem? Thank you! Geesh!

[CornedBee]

I can imagine two reasons why fseek should assert:
a) the FILE* you pass is NULL
b) the third argument is an invalid value

a happens when fopen fails, that is, either the file you specified does not exist and you have a don't create mode (like "r"), or the mode you specified is invalid (like "sdf" would be, but "r" could be too, maybe you need a b or t afterwards ("rt" or "rb")),

b happens because there are only three valid values: SEEK_SET, SEEK_END and SEEK_CUR. Those are defines for numeric values, and 0 just might not be one of them (you should use the symbolic names anyway).

BTW the return value is of type int and only reports errors.

[dubae524]

Ah that explains alot. I think it would be issue a. This was backwhen, when I didn't know that you were supposed to use two back slashes between each name instead of one in a filename. This explains why it failed to open. Thanks.