C - cs50.h GetString error - c

Question

Hello I am completely new to the world of programming an I am attempting to take Harvard's CS50 course online.
While making my "Hello World" program, I downloaded 'cs50.h' to define GetString and string (at least I think). So this is the code I wrote:
file.c:
#include "cs50.h"
#include <stdio.h>
int main(int argc, string argv[])
{
string name;
printf("Enter your name: ");
name = GetString();
printf("Hello, %s\n", name);
}
However, whenever I try to make file, this happens:
cc file.c -o file
Undefined symbols for architecture x86_64:
"_GetString", referenced from:
_main in file-JvqYUC.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [file] Error 1
Here is a link to the cs50.h file if it can help: http://dkui3cmikz357.cloudfront.net/library50/c/cs50-library-c-3.0/cs50.h
I would like to know why I get this error and how I can fix it. Please help.

Answer 1

It seems that you forgot to download and link to project cs50.c file from http://dkui3cmikz357.cloudfront.net/library50/c/cs50-library-c-3.0/cs50.c
*.h usually contain only declarations. *.c (for C) and *.cpp (for C++) contains implementations.
There is GetSting function implementation from this class:
string GetString(void)
{
// growable buffer for chars
string buffer = NULL;
// capacity of buffer
unsigned int capacity = 0;
// number of chars actually in buffer
unsigned int n = 0;
// character read or EOF
int c;
// iteratively get chars from standard input
while ((c = fgetc(stdin)) != '\n' && c != EOF)
{
// grow buffer if necessary
if (n + 1 > capacity)
{
// determine new capacity: start at 32 then double
if (capacity == 0)
capacity = 32;
else if (capacity <= (UINT_MAX / 2))
capacity *= 2;
else
{
free(buffer);
return NULL;
}
// extend buffer's capacity
string temp = realloc(buffer, capacity * sizeof(char));
if (temp == NULL)
{
free(buffer);
return NULL;
}
buffer = temp;
}
// append current character to buffer
buffer[n++] = c;
}
// return NULL if user provided no input
if (n == 0 && c == EOF)
return NULL;
// minimize buffer
string minimal = malloc((n + 1) * sizeof(char));
strncpy(minimal, buffer, n);
free(buffer);
// terminate string
minimal[n] = '\0';
// return string
return minimal;
}

Answer 2

Look at your first include statement. You are using " " instead of < >.

Answer 3

In the videos with the CS50 course, the instructor uses carets (< >) rather than quotation marks (" ").

Answer 4

For anyone taking the CS50 class, and don't want to paste the .c code every time, you can also link the CS50 code when compiling.
Place cs50.h and cs50.c in the same directory as file.c, and then type the following in the command line:
clang file.c -lcs50 -o <file name>
The "-l" links the cs50.c and cs50.h files to your c file (after compiling to object file), and "-o" specifies where to put the compiled output.
More information on this here

Answer 5

In your #include"cs50.h" header you should be typing it like this: #include<cs50.h>. Also, try doing:
#include<cs50.h>
#include<stdio.h>
int main(void)
{
string name = get_string("Enter your name: ");
printf("%s\n", name);
}
Instead of this:
#include "cs50.h"
#include <stdio.h>
int main(int argc, string argv[])
{
string name;
printf("Enter your name: ");
name = GetString();
printf("Hello, %s\n", name);
}
That should get rid of the error messages.
P.S
In week 2 they tell you about help50, but if you want you can use it now.
I myself have found it very useful. Here's how it works: in your terminal window(the one where you execute ./hello and clang) you should type : "help50 make hello" (without the quotation marks) and then it will type: asking for help... in yellow. Then it will decipher the error message and type it in a more simple language. For example:
#include <stdio.h>
#include <cs50.h>
int main(void)
{
string name = get_string("Enter your name: ");
printf("%s\n", name)
}
I do make hello, and this appears:
clang -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wshadow hello.c -lcrypt -lcs50 -lm -o hello
hello.c:13:21: error: expected ';' after expression
printf("%s\n", name)
^
;
1 error generated.
<builtin>: recipe for target 'hello' failed
make: *** [hello] Error 1
But when I do it with help50 make hello, this appears:
clang -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wshadow hello.c -lcrypt -lcs50 -lm -o hello
hello.c:13:21: error: expected ';' after expression
printf("%s\n", name)
^
;
1 error generated.
<builtin>: recipe for target 'hello' failed
make: *** [hello] Error 1
Asking for help...
hello.c:13:21: error: expected ';' after expression
printf("%s\n", name)
^
;
Are you missing a semicolon at the end of line 13 of hello.c?
As you can see, now I know my problem and can fix it. Help50 deciphers the error messages into a language you can understand.