Adding a header file to Xcode

Question

I'm trying to add a C library to Xcode. I downloaded the library from an online C class, and the zipped file contains two files: cs50.c and cs50.h.

I installed these files using the following commands:

gcc -c -ggdb -std=c99 cs50.c -o cs50.o
ar rcs libcs50.a cs50.o
rm -f cs50.o
chmod 0644 cs50.h libcs50.a
sudo mv cs50.h /usr/include
sudo cp libcs50.a /usr/lib

When building the project, I get the following error message:

Undefined symbols for architecture x86_64:
"_GetString", referenced from:
_main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

This is how I'm referencing the header file in my program:

#include </usr/include/cs50.h>

If I don't include the path, I get a can't find file message.

My version of Xcode is: Version 4.5.2 (4G2008a) and I'm running OS X 10.7.5.

Thanks for any suggestions.

Update:

Answer 1

If you trying to use gcc to compile the cs50.h library, I have found that to be unsuccessful on most modern 64 bit macs. Xcode 4.x generally wants a 64 bit compatible library format. GCC has not been updated to include 64 bit object files. Clang/LLVM is a rising alternative to gcc, and is used by Apple for Xcode as their preferred compiler engine. I have not personally tried it yet, but will be exploring Xcode to produce a compatible library for Xcode. I am taking the Harvardx cs50x course at edX, and it is great course, even for experienced programmers. The cs50.h library is interesting, because it provides relatively robust I/O routines for various variable types, e.g. String, Integer. float for the c programming language, including good protection for buffer overflow attacks. You are actually building a custom dynamic library to be added to Xcode, which is also known as a framework. If you have apple developer account, check out the framework programming guide, it should prove useful.

Answer 2

As a general rule, you should never install or modify anything in /usr unless you have a very good reason to do so. This directory is reserved for the operating system, and you can quickly run into a lot of problems - for instance if you accidentally overwrite a system library or header file and even installing new things in there may cause problems when updating your operating system.

If you really need to install this system-wide, then put it into /usr/local.

However, since you compiled the library with debugging information, I assume that you also want to test and play around with it in your project.

To do that, it's much easier to add the sources as a new "C/C++ Library" target to your project. Then Xcode will take care of all the ugly details such as compiling, choosing the right processor architecture (32 or 64 bit), you'll get source-level debugging support in Xcode and if you ever want to install your app or create a package for it, then Xcode will also automatically bundle the dependencies for you.