Have you ever encountered this error when building a program?
Or you are currently experiencing this error in your program. The simple explanation for this error is that you are referencing a symbol in your source code, but the linker cannot find it’s implementation during the linking phase.
This article mainly covers the case if you are using the C family of programming languages. But this error can happen in other languages too. For example, if you are using Ruby, chances are that a native gem requires building on your machine and spits out a similar error. It may not be a direct Ruby problem, but of course you should fix it.
I have encountered the error in Swift, Objective-C, and Ruby. I hope this article helps you solve your problem too 🙌.
There are many reasons why this error can happen. In this article, you will learn how errors happen when you build a C program. After you read this article, you will have a general idea of why the error happened and can draw a relation between it and your error.
In the world of C programming, a linker plays a vital role during program building. An error that usually puzzles developers is the “Symbol not found for architecture” error. This error occurs when you import a header but fail to link to the implementation during linking.
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You will explore the cause of the error and discuss the potential solution here:
Understanding the Linking Process
Compiling a C program is typically divided into separate compilation units. Each consisting of a source file and a header file. This header file is what you import. It only contains function prototypes and declarations. During the linking phase, the linker connects the header and implementation together to create the final executable.
Read More: Why does C and C++ Needs Header File?
The "Symbol not Found for Architecture" Error
This error occurs when you import a function from a header but the linker fails to find its implementation. Your IDE may not report an error because it can find the function in the header file. But Linker cannot be sure that the function you refer to exists.
Causes of the Error:
There are several potential causes for this error, including:
- Missing Implementation: You import the header, but you don't provide the implementation. This could be the file removed, not included in compilation units, having the wrong filename, etc.
- Incorrect Function Signature: The Function signature is how the function in the header and implementation match. The return type, parameter type, and name in both the header and implementation must be the same. A slight difference can cause the symbol to not be found during linking.
- Compiler Flags or Build Settings: If you employ a build flag, it can selectively filter out some lines in your code. The implementation file may exist and be included in the compilation unit, but the code being linked is not included because the compiler skips it.
The above causes are not exhaustive. Especially if you employ a different build system that requires special handling. But for any errors that may occur, it can be rooted back to the causes above.
Solutions:
- Check for Implementation: You must ensure that headers and implementation exist during project compilation. If your build system uses a temporary build directory, those files must exist in that directory.
- Verify Function Signatures: Always check that the function signature matches the header and implementation files. There is no room for inconsistencies.
- Review Compiler Flags and Build Settings: If you use a compiler flag, ensure that the flag doesn’t skip your implementation code.
Something you may need to learn:
Reproduce The Error
You may want to reproduce the issue above to get a better understanding. Here’s the code that you can use to reproduce the “Symbol not found for architecture” error.
main.c
#include "printMessage.h" int main() { printMessage(); return 0; }
printMessage.h
#ifndef PRINT_MESSAGE_H #define PRINT_MESSAGE_H void printMessage(); #endif
printMessage.c
#include <stdio.h> void printMessage() { printf("I am printed from the implementation file.\\n"); }
In the above example, there are three files: main.c, printMessage.h, and printMessage.c. The program is basically calling the
printMessage function and should print “I am printed from the implementation file” in the console. main.c imports the printMessage function from printMessage.h, while the printing logic resides inside printMessage.c.You can compile those files using GCC on a Unix-based system:
gcc main.c printMessage.c -o program
After successful compilation, you can run the program:
./program
The output should be:
I am printed from the implementation file.
If you remove
printMessage.c from the compilation process, you will find the “symbol not found for architecture” error during the linking phase.gcc main.c -o program
Conclusion
Debugging “symbol not found for architecture” is frustrating for the first time. But understanding its causes and implementing the appropriate solution can help you resolve the issue faster. Ensuring that the header and implementation files exist and verifying the function signature can help you overcome this error in the future.
Keep learning!