释放结构内的内存时程序崩溃

Question

I have file parsing program which is like this, my program crashes when freeing memory. I have to check if the value is empty then i have to free the other malloced variable.

struct db_handle_st {
    char *server;
    char *user;
};

int main()
{   
    char srv_conf_file[] = "C:\\\\Users\\admin\\Documents\\Visual Studio 2010\\Projects\\abcd\\abcd\\service.config";
    FILE *fp = NULL;
db_handle_st db_details;
fp = fopen(srv_conf_file, "r");
    if (fp != NULL) {
        /* Look for key value pairs. */
        while (fgets(line, sizeof(line), fp) != NULL) {
            /* Get key */
            key = line;
            key[strlen(key) - 1] = '\0'; /* trim the newline. */
            if ((value = strstr(line, "=")) != NULL) {
                *value = '\0';
                value++;
            }
            if (key && value)
                printf("    %s: %s\n", key, value);
            else
                continue;
            if (!strncmp(key, "SERVER", strlen("SERVER"))&&(strcmp(value,""))) {
                /*  if(strcmp(value,"")==0) {
                goto err;
                }*/
                db_details.server = (char *)malloc(strlen(value)+1);
                strcpy(db_details.server, value);
                printf("db_details.server is %s\n",db_details.server);
            }
            if (!strncmp(key, "USER", strlen("USER"))&&(strcmp(value,""))) {
                db_details.user = (char *)malloc(strlen(value)+1);
                strcpy(db_details.user, value);
                printf("db_details.user is %s\n",db_details.user);
            }
}
}
if((db_details.user!=NULL) || (db_details.server!=NULL)) {
        printf("something is zero\n");
        if(db_details.user) {
            free(db_details.user);}
        if(db_details.server) {
            free(db_details.server);}
    }
}

My config looks like this

SERVER=localhost
USER=

When i run this program i get the

"something is zero" and the program crashes.

Answer 1

You need to initialize the char pointers in the struct db_handle_st to NULL otherwise you might free some random data (their value is undefined otherwise) and this will cause the crash.

PS: You do not need to check for NULL before calling free ( free on NULL just does nothing) also you should fclose the file you opened.

Answer 2

You never initialized db_handle_st db_details; so the pointers are indeterminate, and the crash indicates that the indeterminate value was not a null pointer.

Use:

db_handle_st db_details = { 0, 0 };