CODEWITHSUNDEEP
cgcc
He-Man
He-Man

Reputation: 75

Errors when using GCC to compile C code provided in textbook

I'm a CS student about to start my second year. In preparation, I'm reading "An Introduction to C Programming for Java Programmers" by Mark Handley.

In it I found this code, that I decided to try out for myself:

#include <stdlib.h>
main()
{
char *s1;
char s2[80];
char *s3;
s1 = "Hello";
s3 = malloc(80);
printf("Enter your first name:\n");
fgets(s2, 80, stdin);
printf("Enter your last name:\n");
fgets(s3, 80, stdin);
printf("%s %s %s\n", s1, s2, s3);
free(s3);
}

I get the following errors when trying to compile with GCC:

strings.c: In function ‘main’:
strings.c:11: warning: incompatible implicit declaration of built-in     `
`function ‘printf’
strings.c:12: error: ‘stdin’ undeclared (first use in this function)
strings.c:12: error: (Each undeclared identifier is reported only once
strings.c:12: error: for each function it appears in.)

Like I said, this is code copied right from the text, so I'm a little frustrated it doesn't work. I figure this must do with the version of GCC. If anyone could help me move in the right direction to understand what is going on here, I would appreciate it. Thanks!

Update: Changed the code per the helpful suggestions below, and it works. It didn't explicitly say to try this code in the text, I took it upon myself to do that. I think the author just intended to show how strings can be handled in C, and how that is different from Java. Thanks everyone, I really appreciate it!

Upvotes: 1

Views: 1500

Answers (2)

ameyCU
ameyCU

Reputation: 16607

1. Include header <stdio.h> (in which printf , fgets are defined)

2. main() -> int main(void) or int main(int argc, char **argv)

3. add return 0; (indicating success and a good practice).

Upvotes: 3

PC Luddite
PC Luddite

Reputation: 6088

Your code relies on an implicit declaration of printf, fgets, and stdin, and an old signature for main(). It doesn't compile because it's not currently valid C (it's not even valid C89, the first C standard).

You need to include stdio.h where these definitions are located. GCC allows you to use that signature for main() as an extension, but it's still not technically valid C.

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

int main(void)
{
    char *s1;
    char s2[80];
    char *s3;
    s1 = "Hello";
    s3 = malloc(80);
    printf("Enter your first name:\n");
    fgets(s2, 80, stdin);
    printf("Enter your last name:\n");
    fgets(s3, 80, stdin);
    printf("%s %s %s\n", s1, s2, s3);
    free(s3);
    return 0; /* not necessary, but it's good practice */
}

Upvotes: 2

Related Questions