Identify the Issue
- Check for typographical errors in the function definition of
main(). Ensure it is correctly typed and the necessary opening and closing braces are present.
- Confirm that the
main() function signature is correctly defined. For C++, the acceptable signatures are int main() or int main(int argc, char \*argv[]).
- Ensure the source file containing
main() is included in the list of files to be compiled and linked. Missing files in the build setup can lead to this error.
Check the Build System
- Verify that your build system (e.g., Makefile, CMake) is properly configured to include all source files. Missing source files result in an undefined reference to
main.
- In complex firmware projects, ensure all necessary directories containing source files are added to the compiler's search path. Use appropriate flags such as
-I for include paths and -L for library paths.
- Review linker settings in the build system configuration. Incorrect linker scripts or options can lead to the linker not finding the
main() entry point.
Correct Linker Script
- If your firmware project uses a custom linker script, verify that it defines the correct entry point. The entry point should be set to
main or the appropriate starting function for your application context.
- Consult the microcontroller or processor's documentation for any unique entry point requirements. Some architectures may demand specific linker script configurations.
Check Preprocessor Directives
- Examine any preprocessor directives related to
main(). Conditions within #ifdef or #ifndef directives can exclude the definition of main.
- Ensure that any macros or defines used around the
main function are correct. Unintended macro expansions might alter the function signature or make it unavailable.
Compiler and Toolchain Issues
- Make sure the correct compiler and toolchain versions are used. Using an incompatible version might cause issues specific to function definitions or entry point expectations.
- Verify the command-line arguments passed to the compiler. Options that tweak function name handling or linkage, such as optimization settings, can result in undefined references if misconfigured.
Common Errors in Embedded Systems
- In firmware and embedded environments, especially those without standard libraries, ensure that your own initialization code leads to a
main function or equivalent entry point.
- Implement any necessary startup routines or assembly code that is specific to bare-metal development, ensuring they correctly transfer control to
main().
