How to check dynamic allocation

Question

How can i check if i am using right the dynamic allocation in my C code. It is an assignment for uni. When i put my code in the auto corrector system of my professor i get an error for dynamic allocation. My code :

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <stdarg.h>
#include <sys/types.h>
#include <unistd.h>
#include <ctype.h>
int main( )
{

    for(;;)
    {
        char *cmd,*splitcmd;
//*pr0,*pr1,*pr2 ;
    size_t bufsize = 1024;
        char pr1[bufsize];
        char pr2[bufsize];
        char pr0[bufsize];
        //char pr3[40];
        int i,j,nargc=0,characters;
        char **cmdArray;
        //size_t bufsize = 1024;
        // size_t bufsizecmd =1024;
        pid_t pid,wpid;
        int status = 0;
        char pr='$';
        char exit1[10]="exit";
        char *path;
        path = getenv("PATH");

        putchar(pr);


        cmd = malloc(bufsize * sizeof*cmd);
        characters = getline(&cmd,&bufsize,stdin);
//printf("cmd===> %s  characters===>  %d \n",cmd,characters);
        if(cmd[characters-1]=='\n' )
        {
            cmd[characters-1]='\0';
            characters--;
        }
//printf("cmd===> %s  characters===>  %d \n",cmd,characters);


        cmdArray = malloc(bufsize*sizeof*cmdArray );
        for ( i = 0; i < bufsize; i++ )
        {
            cmdArray[i]=malloc(bufsize*sizeof*cmdArray );
        }

        splitcmd=strtok(cmd," ");
        // printf(" cmd====  %s\n",cmd);
        while((splitcmd))
        {
            strcpy(cmdArray[nargc],splitcmd);
            if(cmdArray[nargc][(strlen(cmdArray[nargc]))-1]==' ')
                cmdArray[nargc][(strlen(cmdArray[nargc]))-1]='\0';
//printf(" nargc====%d  cmdArray===[%s] \n",nargc,cmdArray[nargc]);
            nargc++;
            splitcmd = strtok(NULL," ");
        }


//printf(" pr0  %s   \n",pr0);
//printf(" pr1  %s   \n",pr1);
//printf(" pr2  %s   \n",pr2);

        strcpy(pr0,cmdArray[0]);
        if (strcmp( pr0, exit1) == 0 )
        {
            //printf("---------->Eksodos apo to programma<---------- \n");
        free(cmd);
            return (0);
            exit(0);

            //return (0);
        }
        else
        {


            if ((pid=fork()) == 0)
            {
                if(nargc ==1 )
                {
                    strcpy(pr0,cmdArray[0]);
                    char *argv[] = {path,NULL};

                    execvp(pr0,argv);

                    for ( i = 0; i < bufsize; i++)
                    {
                        free(cmdArray[i]);
                    }
                    free(cmdArray);
            free(cmd);
                    exit(0);
                }
                else if(nargc==2)
                {
                    strcpy(pr0,cmdArray[0]);
                    strcpy(pr1,cmdArray[1]);
                    char *argv[] = {pr0,pr1,NULL};

                    execvp(pr0,argv);
                    exit(0);

                    for ( i = 0; i < bufsize; i++)
                    {
                        free(cmdArray[i]);
                    }
                    free(cmdArray);
            free(cmd);
                    exit(0);
                }
                else
                {

                    strcpy(pr0,cmdArray[0]);
                    strcpy(pr1,cmdArray[1]);
                    strcpy(pr2,cmdArray[2]);

                    //printf("cmdddddddd****====%s \n",*cmdArray);
                    char *argv[] = {pr0,pr1,pr2,NULL};

                    execvp(argv[0],argv);

                    for ( i = 0; i < bufsize; i++)
                    {
                        free(cmdArray[i]);
                    }
                    free(cmdArray);
            free(cmd);
                    exit(0);
                }
            }

            wait(&status);

        }

    }
}

In C, you don't cast malloc. http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc — meskobalazs, Nov 27 '15 at 17:49
Trace the memory allocation and freeing using mtrace (http://www.gnu.org/software/libc/manual/html_node/Tracing-malloc.html#Tracing-malloc). There is a nice tutorial here - http://man7.org/linux/man-pages/man3/mtrace.3.html — Kishore, Nov 27 '15 at 17:55
I edit my code. But still i am getting the same message. Am i doing it right? @coderredoc — Spyros_av, Nov 27 '15 at 18:40
I dont know. When i asked him he told me that the problem is that my code isn't doing dynamic allocation in memory. @coderredoc — Spyros_av, Nov 27 '15 at 19:28

Duane McCully · Answer 1 · 2015-11-28T04:43:18.940

There is no corresponding free() for cmd = (char *)malloc(bufsize * sizeof(char));.

Also, this code block:

strcpy(pr0,cmdArray[0]);
if (strcmp( pr0, exit1) == 0 )
{
    //printf("---------->Eksodos apo to programma<---------- \n");
free(cmd);
    return (0);
    exit(0);
     //return (0);
}

will need this

for ( i = 0; i < bufsize; i++)
{
    free(cmdArray[i]);
}
free(cmdArray);

before the

free(cmd);

In this code block, there are two exit() calls:

else if(nargc==2)
{
    strcpy(pr0,cmdArray[0]);
    strcpy(pr1,cmdArray[1]);
    char *argv[] = {pr0,pr1,NULL};

    execvp(pr0,argv);
    exit(0);

    for ( i = 0; i < bufsize; i++)
    {
        free(cmdArray[i]);
    }
    free(cmdArray);
free(cmd);
    exit(0);
}

The one immediately after the execvp(pr0,argv); prevents any of the free() calls from being executed. It needs to be removed.

Thanks for the help. But still the same error message. – Spyros_av Nov 28 '15 at 14:03 — Spyros_av, Nov 28 '15 at 14:03

How to check dynamic allocation

1 Answers1