How to Fix: Warning/error "function declaration isn't a prototype"
Error: function declaration isn't a prototype. Solution: Provide implementation for function or use extern keyword correctly.
📋 Table of Contents
The warning/error 'function declaration isn't a prototype' occurs when you are trying to declare a function as both a function and an external variable in the same scope. In your case, the problem lies in the definition of `testlib()` in `mylib.c` where it's declared as `extern int testlib();`. This indicates that `testlib()` is only defined elsewhere (i.e., not in the current file), but you are trying to use its address by calling `testlib()`. To fix this, remove the `extern` keyword from the declaration of `testlib()` and define it as a regular function. Here's how your corrected code shouldlook like:
🔧 Proven Troubleshooting Steps
Method 1: Correct Declaration
- Step 1: Remove the `extern` keyword from the declaration of `testlib()` in `mylib.h`. The corrected code should look like this:
Method 2: Correct Implementation
- Step 1: Define `testlib()` as a regular function in `mylib.c`. The corrected code should look like this:
💡 Conclusion
By following these steps, you will be able to successfully compile and run your program.
❓ Frequently Asked Questions
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