Undefined reference to memset

Question

I wrote simple c program using system call and it worked fine when I compiled it with gcc. But when I tried to generate shell code (shellforge) using command

./sf.py username.c

I got error stating

Undefined reference to memset

How to resolve this? Here is my code

#define O_CREAT     0100
#define O_WRONLY    01
#define O_APPEND    02000
#define IDLEN 100
int main(void)
{
    char user_name[IDLEN]="";
    char pass1[IDLEN]="";
    char pass2[IDLEN]="";
    int fd,a,b,c;

    //to give user direction
    char user[]="Please type your username and hit enter:\n";
    char p1[]="Please type password and hit enter:\n";
    char p2[]="Please type password and hit enter:\n";

    write(1,user,sizeof(user));
    a=read(0,user_name,IDLEN);
    user_name[a-1]='\0';
    while(1)
    {
        write(1,p1,sizeof(p1));
        b=read(0,pass1,IDLEN);
        pass1[b-1]='\0';
        write(1,p2,sizeof(p2));
        c=read(0,pass2,IDLEN);
        pass2[c-1]='\0';

        int temp=0;
        while(pass1[temp] == pass2[temp])
        {
            if(pass1[temp] == '\0' || pass2[temp] == '\0')
            {
                break;
            }
            temp++;
        }
        if(pass1[temp] == '\0' && pass2[temp] == '\0')
        {
            break;
        }else{
            char error[] = "password does not match! please type your password again";
            write(1,error,sizeof(error));
        }
    }

    fd = open("user.txt",O_CREAT|O_WRONLY|O_APPEND,0666);
    if(fd<0)
    {
        return 1;
    }

    char file_user[]="\nUsername:";
    char file_pass[]="\nPassword:";
    write(fd,file_user,sizeof(file_user)-1);
    write(fd,user_name,a-1);
    write(fd,file_pass,sizeof(file_pass)-1);
    write(fd,pass1,b-1);
}

Why? OP doesn't include `memset` in his code. Regardless, OP doesn't have the include for `write` and `read`. Why would gcc not return an error for this? Why would shellforge then return an error for memset, but not this? — Daniel Margosian, Jul 27 '16 at 21:15
adding string.h is giving other errors nw file:///home/ubuntu/Desktop/Screenshot%20(789).png — surendra, Jul 27 '16 at 21:22
gcc is not required to issue errors for calling functions before declaring them for compatibility reasons to pre C89 code. If you use a function before declaring them, it assumes the function returns int and infers the types of the arguments based on the call. See http://stackoverflow.com/a/2575186/3914029 — miravalls, Jul 27 '16 at 21:25
yes it works fine when I execute it using gcc but it gives error only when i am trying to execute it using shellforge — surendra, Jul 27 '16 at 21:26
Which version of shellforge are you using? depending on the sflib version you're using, the memset() may be implicitly called under the system call wrappers defined in the shellforge include headers. — pah, Jul 27 '16 at 21:29

score 5 · Accepted Answer · answered Jul 27 '16 at 21:32

5

include <string.h>; memset() is usually a macro and not a symbol in the standard libraries.

EDIT: although not called explicitly, the compiler might call it for char user_name[IDLEN]=""; and the other string variables.

You should compile with '-W -Wall' to detect such issues.

answered Jul 27 '16 at 21:32

ensc

6,704
14
22

Did this actually fix the issue? – user253751 Jul 27 '16 at 23:24
this anser indeed gave me hint and i have also added answer about what changes I had done. – surendra Jul 28 '16 at 06:45

score 2 · Answer 2 · answered Jul 27 '16 at 21:58

2

I modified my code from

char user_name[IDLEN]="";
char pass1[IDLEN]="";
char pass2[IDLEN]="";

to

char user_name[IDLEN];
char pass1[IDLEN];
char pass2[IDLEN];

and it worked like a charm! :)

answered Jul 27 '16 at 21:58

surendra

119
1
2
9

Undefined reference to memset

2 Answers2