Is argv[] terminated by a NULL string?

[dwks]

Is it true that argv[] is terminated by a NULL string? Like

Arguments:

argv[0] = "program"
argv[1] = "arg1"
argv[2] = "arg2"
argv[3] = ""

So can you go

int x;
for(x = 0; argv[0][0]; x ++) {
    /* ...code...*/
}

Instead of

int x;
for(x = 0; x < argc; x ++) {
    /* ...code... */
}

Because then I can pass one less parameter to my argument validating function(s).

[quzah]

int x;
for(x = 0; argv[0][0]; x ++) {
    /* ...code...*/
}

Um, no. I think you mean:

#include<stdio.h>
int main( int argc, char *argv[] )
{
    size_t x;

    for( x = 0; argv[ x ]; x++ )
        printf("argv[ %d ] is %s\n", x, argv[ x ] );

    return 0;
}

Otherwise, all you're doing is testing the first argument's first character over and over and over. (Indefinately.) Then X overflows itself, and starts to wrap around, which really has no effect, other than to keep on going forever and ever and...


Quzah.

[dwks]

Sorry, a typo . . . but you're wrong too.

#include<stdio.h>
int main( int argc, char *argv[] )
{
    size_t x;

    for( x = 0; *argv[ x ]; x++ )  /* need a * here */
        printf("argv[ %d ] is %s\n", x, argv[ x ] );

    return 0;
}

Otherwise you're testing the address of the current string.

[quzah]

Run it. But to answer your question, no there is not an extra string of nothingness.


Quzah.

[Salem]

argv[argc] is NULL, not ""

[dwks]

Oh, sorry quzah, I thought argv[argc] was "".

But is argv[argc] guarenteed to be NULL? Like, is it part of the standard?

[Dave_Sinkula]

But is argv[argc] guarenteed to be NULL? Like, is it part of the standard?

Yes.

[dwks]

Thanks for the clarification.

[gnncj]

Sorry, a typo . . . but you're wrong too.

#include<stdio.h>
int main( int argc, char *argv[] )
{
    size_t x;

    for( x = 0; *argv[ x ]; x++ )  /* need a * here */
        printf("argv[ %d ] is %s\n", x, argv[ x ] );

    return 0;
}

Otherwise you're testing the address of the current string.

Should be for( x = 0; argv[ x ]; x++ ) , not for( x = 0; *argv[ x ]; x++ ) . otherwise it will cause a segmentation fault.

[dwks]

That's already been pointed out. I thought argv[argc] was "", but in reality it is NULL. The * would be required if argv[argc] was "".