why does the following program give error when it is checked with cppcheck analyzer

Question

#include "stdio.h"

int main (void) {
    char xx[1000] = "hello";
    sprintf (xx, "xyzzy plugh %s", xx);
    printf ("%s\n", xx);
    return 0;
}

::::(error) Undefined behaviour: xx is used wrong in call to sprintf or snprintf. Quote: If copying takes place between objects that overlap as a result of a call to sprintf() or snprintf(), the results are undefined.

Simon Richter · Accepted Answer · 2011-03-08 12:36:50Z

1

Precisely what it says. You are passing the same array both as input and output to sprintf(), which is not a supported usage as there is no guarantee that sprintf will write the output string in ascending order.

answered Mar 8, 2011 at 12:36

Simon Richter

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1 Comment

Wouter Simons Over a year ago

It also makes very little sense to do this in this way. Normally you have a char array to receive the formatted strings and the parameters to your format string as parameters coming from something. Perhaps update your function to take console args and put those in to do the string formatting and use snprintf to make it safe for overflow situations.

Community · Accepted Answer · 2017-05-23 11:55:24Z

1

You are writing into char array xx as well as using it as the source for the copy. This behaviour is undefined. Here's an existing question about the situation:

Is sprintf(buffer, "%s […]", buffer, […]) safe?

edited May 23, 2017 at 11:55

CommunityBot

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answered Mar 8, 2011 at 13:06

Ant

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