Question

I have recently made a program that is supposed to take two environment variables, insert them into a string, then send the string to popen, and it works fine most of the time, but for some reason it will randomly not execute every so often, so I was just wondering if anyone saw any possible errors or mistakes that I am making?

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

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

   char *output;
   char *ccode;
   char *command;
   char *log;

   command = malloc(1024);
   log = malloc(1024);
   const char *parg = getenv("MCEXEC_ARGS");
   const char *pname = getenv("MCEXEC_PLAYERNAME");

   if(strcmp(parg,"")==0) {
       output = "Usage: /staff <message>";
       printf( "%s\n", output );
       return 0;
   }

   freopen("/dev/null","w",stdout);

   if (argv[1] == NULL) {
       snprintf(command, 1024,
                "/home/minecraft/remoteclient01a.py 'sendmsgtogroup staff §f(§bSTAFF§f) <%s§f> %s'",
                pname, parg);
       snprintf(log, 1024,
                "/home/minecraft/remoteclient01a.py 'savetolog info staffmsg: <%s> %s'",
                pname, parg);
   }
   else if (strcmp(argv[1],"me")==0) {
       snprintf(command, 1024,
                "/home/minecraft/remoteclient01a.py 'sendmsgtogroup staff §f(§bSTAFF§f) * %s§f %s'",
                pname, parg);
       snprintf(log, 1024,
                "/home/minecraft/remoteclient01a.py 'savetolog info staffmsg: * %s %s'",
                pname, parg);
   }

   popen(command, "w");
   popen(log, "w");

   free(command);
   free(log);

   return 0;
}

Answer 1

Well …

• You’re not checking that malloc() succeeds.
• You’re not handling that the environment variables might not exist.
• You’re calling strcmp() on a pointer that might be NULL; which might kill your program right there.
• You’re not checking that the file open succeeds.
• You have weird § characters in the commands strings, not sure if those are intended.
• You’re not checking if popen() succeeds.
• I don’t think your usage of popen() makes sense; you’re not using the pipes once opened.