C - cs50.h GetString error

问题

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.

回答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;
}

回答2:

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

回答3:

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

回答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

来源：https://stackoverflow.com/questions/22052468/c-cs50-h-getstring-error

标签

string

cs50