Fixing Undefined Symbols for Architecture x86_64 in C++: A Comprehensive Guide

When you work with C++ on macOS or Linux, you might come across an error message like this:

Undefined symbols for architecture x86_64

In this guide, we'll explore why this error occurs and provide step-by-step instructions to fix it. We'll also cover some common questions related to this issue in the FAQ section.

Table of Contents

  1. Understanding the Error
  2. Step-by-Step Solution
  3. FAQ
  4. Related Links

Understanding the Error

Undefined symbols for architecture x86_64 occur when you try to link object files or libraries that have been compiled for different architectures. This typically happens when some of the source files or libraries being used in the project were compiled with incompatible options or for a different target platform.

In C++, the linker combines object files and libraries to create an executable or a shared library. If the linker cannot find a definition for a symbol (like a function or a variable) referenced in one of the object files, it will throw an "undefined symbol" error.

Step-by-Step Solution

Here's a step-by-step guide to fix the "Undefined symbols for architecture x86_64" error:

Step 1: Identify the Undefined Symbols

First, take note of the undefined symbols mentioned in the error message. For example:

Undefined symbols for architecture x86_64:
  "_someFunction", referenced from:
      _main in main.o

In this case, the undefined symbol is _someFunction.

Step 2: Locate the Source File or Library

Next, find the source file or library containing the definition of the undefined symbol. This could be a source file you wrote yourself or a third-party library you're using.

Step 3: Check Compilation Options

Ensure that the source file or library containing the undefined symbol is compiled with the same options and target platform as the rest of your project. If you're using a build system like CMake, make sure the target platform and compiler options are consistent across your entire project.

Step 4: Rebuild the Project

After making any necessary changes to your compilation options, rebuild your project to see if the error has been resolved. If the error persists, you may need to clean your build directory and build the project from scratch.


1. Can this error occur on platforms other than x86_64?

Yes, this error can occur on other platforms, such as ARM or i386. The error message will specify the architecture that has undefined symbols. For example:

Undefined symbols for architecture arm64:

2. How can I find out which architectures my object files or libraries are compiled for?

You can use the file command on Linux or macOS to find out the architectures of your object files or libraries. For example:

file someFile.o

3. Can this error occur if I'm using a prebuilt third-party library?

Yes, if the prebuilt third-party library is not compiled for the same architecture as your project, you may encounter the "undefined symbols" error. In such cases, you should either find a version of the library compiled for your target architecture or build the library from source with the appropriate options.

4. What if the undefined symbol is from a system library?

In this case, ensure that you're linking against the correct version of the system library. You may need to adjust your linker flags or library search paths to point to the correct version.

5. What if I still can't resolve the error after following the steps above?

If you're still having trouble, consider seeking help from online forums or communities related to C++ development or the specific libraries you're using. They may be able to provide further guidance or insight into your specific issue.

  1. Stack Overflow: Undefined symbols for architecture x86_64
  2. Apple Developer Forums: Undefined symbols for architecture x86_64
  3. CMake: Cross Compiling for Different Architectures
  4. GCC: Specifying Target Machine and Compiler Options
  5. Apple Developer Documentation: Building for Multiple Architectures

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