Access violation reading location 0x00000000. with argv[]

Question

I am running the following program and got errors:

First-chance exception at 0x0f32d440 (msvcr100d.dll) in c.exe: 0xC0000005: Access violation reading location 0x00000000.
Unhandled exception at 0x772815de in c.exe: 0xC0000005: Access violation reading location 0x00000000.
The program '[9048] c.exe: Native' has exited with code -1073741510 (0xc000013a).

Here is the code

#include <string.h>
#include <stdio.h> 
#include <stdlib.h> 
int main(int argc, char *argv[], char *env[]) //char *argv[] 
{ 
int i; 

printf("These are the %d command- line arguments passed to main:\n\n", argc); 
if(strcmp(argv[1],"123")==0)                
    {
        printf("success\n");
     }
else
for(i=0; i<=argc; i++) 
    //if(strcmp(argv[1],"abc")==0)

    printf("argv[%d]:%s\n", i, argv[i]);
/*printf("\nThe environment string(s)on this system are:\n\n"); 
for(i=0; env[i]!=NULL; i++) 
printf(" env[%d]:%s\n", i, env[i]);*/ 
system("pause");
} 

The problem should be with the strcmp function but I dont know how to solve it. Could anyone help?

Answer 1

You have (at least) two problems.

The first is doing this:

if(strcmp(argv[1],"123")==0) 

without first checking that argc >= 2.

The second is this:

for(i=0; i<=argc; i++) 

in that you should be processing arguments 0 thru argc - 1 inclusive. What that loop does is process arguments 0 through argc and argv[argc] is always NULL.

The following program illustrates one way to fix this:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main (int argc, char *argv[]) {
    int i;

    printf ("These are the %d command-line argument(s) passed to main:\n", argc);
    if ((argc >= 2) && (strcmp (argv[1], "123") == 0)) {
        printf ("   success\n");
    } else {
        for (i = 0; i < argc; i++)  {
            printf ("   argv[%d] = [%s]\n", i, argv[i]);
        }
    }
    return 0;
}

You can see that the comparison with "123" is only done after ensuring that argv[1] is populated correctly. In addition, the loop has been changed to exclude argv[argc] since that's not one of the arguments. A transcript follows:

pax> testprog
These are the 1 command-line argument(s) passed to main:
   argv[0] = [testprog]

pax> testprog 123
These are the 2 command-line argument(s) passed to main:
   success

pax> testprog a b c
These are the 4 command-line argument(s) passed to main:
   argv[0] = [testprog]
   argv[1] = [a]
   argv[2] = [b]
   argv[3] = [c]