Synopsis

Do not store pointers returned by certain functions.

Enabled by default

Yes

Severity/Certainty

Low/Medium

Full description

Do not store pointers returned by getenv() and similar functions because the string data it points to may be overwritten by a subsequent call to the same function or invalidated by modifications to the environment. This string should be referenced immediately and discarded. If later use is anticipated, the string should be copied so the copy can be safely referenced as needed.

Coding standards

Code examples

The following code example fails the check and will give a warning:

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

void func(void) {
    char *tmpvar;
    char *tempvar;

    tmpvar = getenv("TMP");
    if (!tmpvar) {
        /* Handle error */
    }
    tempvar = getenv("TEMP");
    if (!tempvar) {
        /* Handle error */
    }
    if (strcmp(tmpvar, tempvar) == 0) {
        printf("TMP and TEMP are the same.\n");
    } else {
        printf("TMP and TEMP are NOT the same.\n");
    }
}

The following code example passes the check and will not give a warning about this issue:

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

void func(void) {
    char *tmpvar;
    char *tempvar;

    const char *temp = getenv("TMP");
    if (temp != NULL) {
        tmpvar = (char *)malloc(strlen(temp)+1);
        if (tmpvar != NULL) {
            strcpy(tmpvar, temp);
        } else {
            /* Handle error */
        }
    } else {
        /* Handle error */
    }

    temp = getenv("TEMP");
    if (temp != NULL) {
        tempvar = (char *)malloc(strlen(temp)+1);
        if (tempvar != NULL) {
            strcpy(tempvar, temp);
        } else {
            /* Handle error */
        }
    } else {
        /* Handle error */
    }

    if (strcmp(tmpvar, tempvar) == 0) {
        printf("TMP and TEMP are the same.\n");
    } else {
        printf("TMP and TEMP are NOT the same.\n");
    }
    free(tmpvar);
    free(tempvar);
}