Understanding Undefined Reference Errors in IAR C/C++ Compiler
Undefined reference errors in the IAR C/C++ Compiler typically occur during the linking stage of your build process. This happens when you declare or call a function and the linker cannot find the implementation when it needs to link the binaries. Understanding the root causes and how to fix them is essential for a firmware developer using the IAR Compiler.
Common Causes of Undefined Reference Errors
Missing Object Files: Often, the implementation of a function is in another source file that has not been compiled into an object file or is not included in the linker command.
Missing or Incorrect Library Links: Your implementation might be in an external library that is not linked against your project or is incorrectly specified.
Typographical Errors: A typo in function names either in the declaration or implementation can lead to this error, as they must match exactly.
Incorrect Function Signature: Signature mismatches between function prototype and definition can also result in undefined reference errors.
Namespace Issues in C++: If you are using C++, make sure the function name is in the correct namespace, or is being called with the correct scope.
Steps to Resolve Undefined Reference Errors
- Ensure Source File Compilation: Make sure that all your source files are compiled. Check your IDE's project settings to ensure all relevant files are included. In some cases, you might need to manually add these files to a makefile or build script if your build system relies on them.
Add your .c/.cpp files to the project in IAR through Project settings or any Makefile you are using.
- Check Linker Settings: It is crucial to ensure that all necessary object files (.o) and libraries (.a or .lib) are linked with your project. Use the IAR IDE's options to specify additional libraries or add them directly to your linker flags in a makefile.
#pragma import(__use_no_semihosting) // Example of adding library directives in IAR
- Verify Function Name and Signature: Verify that the function's signature in the declaration matches the definition precisely. A difference in signatures can cause this problem.
// in header file
void myFunction(int param);
// in source file
void myFunction(int param) { /* implementation */ }
Ensure that both function names and parameter types match exactly across your project.
- Adjust C++ Namespaces: In C++, check your namespaces are correctly used. If you have declared a function inside a namespace, be sure to call it with its fully qualified name or using the proper
using directive.
namespace MyNamespace {
void myFunction();
}
// Call this with MyNamespace::myFunction();
- Review External Dependencies: For functions implemented in libraries, ensure that you have correctly specified the path to the external library in your compiler and linker settings.
// In your project setup, ensure library paths are added:
#include "path/to/external/library"
Use IAR Compiler Tools for Debugging
- Verbose Linker Output: Enable verbose output from the linker to get more detailed information on what specific references or functions are causing errors. This can often help pinpoint leading causes that are not immediately obvious from the compile error alone.
// In your linker settings, enable verbose logging:
--log_report
By following these steps and using these strategies, you can efficiently trace and fix undefined reference errors within the IAR C/C++ Compiler environment, ensuring a more seamless development process for your embedded applications.
