newbie: logical && comparison questions

[cstudent]

#include <stdio.h>
int main(int argc, char* argv[])
{
argc--;
++argv;
if(*argv)
{
while(argv[0][0] == ‘-‘ && argv[1] && argv[2])
{

}

return 0;
}

lets say we run it by typing ./hello -argument1 -argument2 -argument3. why does the comparison fail at the while conidition??

argv[1] is -argument2 and argv[2] is -argument2. going by precedence, we comparre argv[0][0] == ‘-‘ && argv[1] first and this fails why?

[Dino]

Do a printf on argv[0] and you'll see why it fails.

[tabstop]

Except for the whole "we've incremented argv" thing. Once argv++ has happened, argv[0] is -argument1 and argv[1] is -argument2 ... and argv[2] is NULL.

[vart]

you should check the argc value before accessing any argv[i] except argv[0]

[Dino]

I missed that. And you missed there are 3 args!

I ran the program. Works for me.

[cstudent]

hmm i found out where my problem is. the comparison should be true but by copying the arguments from pdf to the command line turns -argument into --argument.

Anyway, am i right to say that for logical && operater,

while(argv[0][0] == ‘-‘ && argv[1] && argv[2])

argv[x] will always be true if argv at index x contains non null value.

thanks alot for the fast responses.

[vart]

argv[x] will always be true if argv at index x contains non null value.

Where is it written that the argv[x] could contain a NULL value? if x is >= argc - it is just an out-of-bounds access resulting in undefined behavior

[laserlight]

Where is it written that the argv[x] could contain a NULL value? if x is >= argc - it is just an out-of-bounds access resulting in undefined behavior

Not quite. argv[argc] is a null pointer, according to C99.