No Out Of Bounds error on inside for loop

[Gabriel Anzziani]

No error reported on these two cases, which should report Out of Bound accesses to the array:

Case 1: There is an unkown function that uses the index, however, the index is not being modified
Case 2: The index is modified which causes accessing the array out of bounds

void test(void) {
    int array[4]={1,2,3,4};
// Case 1
    for (int i=1; i <= 4; i++) {
        function(i);
        array[i]=0; // no error!?
    }
// Case 2
    for (int i=0; i < 4; i++) {
        i=i+10;
        array[i]=0; // no error
    }
    // errors below valid
    for (int i=1; i <= 4; i++) {
        array[i]=0;
    }
    printf("%d", array[4]);
}

[Neil Matthews]

Might be similar to https://sourceforge.net/p/cppcheck/discussion/general/thread/2baedb245a/#32cf and https://sourceforge.net/p/cppcheck/discussion/general/thread/06639e9b58/#3b1b

[Daniel Marjamäki]

Thanks for this input. Very valuable. For case 1 Cppcheck really can't warn, because function might change i. If you show the function declaration Cppcheck does warn. You get a warning for this code:

void function(int);

void test(void) {
    int array[4]={1,2,3,4};
// Case 1
    for (int i=1; i <= 4; i++) {
        function(i);
        array[i]=0; // no error!?
    }
}

For case 2.. I believe it's a genuine false negative. We should be able to catch this.

[Gabriel Anzziani]

Thanks for the reply.
For case 1, I was actually doing something like:

#include <stdio.h>
.
.
        printf("%d",i);

And I did not get the warning. Then I noticed it also happened with any unknown function that uses i. Since i is passed by value it is not being modified, cppcheck should notice this.

[Daniel Marjamäki]

hmm.. if you use printf then we should be able to warn.

Since i is passed by value it is not being modified, cppcheck should notice this.

We really can't assume that.

imagine:

#define function(i)   i=0;

void test(void)
{
    int array[4]={1,2,3,4};
    for (int i=1; i <= 4; i++) {
        function(i);
        array[i]=0; // no error!?
    }
}

[Daniel Marjamäki]

If printf is used (or any other standard function that does not modify the value) we should warn. I created ticket https://trac.cppcheck.net/ticket/9478

[Daniel Marjamäki]

I created this ticket for "case 2"
https://trac.cppcheck.net/ticket/9475