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|  How to Fix Error: invalid conversion from 'int' to 'void ()(void)'

How to Fix Error: invalid conversion from 'int' to 'void ()(void)'

October 14, 2024

Discover how firmware developers can solve the C++ error 'invalid conversion from int to void ()(void)' with simple steps and best practices in this comprehensive guide.

How to Fix Error: invalid conversion from 'int' to 'void ()(void)'

 

Understand the Error Message

  • The error indicates that there is an attempt to convert a value from an 'int' type to a 'void (\*)()' type, which is a function pointer to a function taking no parameters and returning nothing. Understand that in C++, implicit conversion between these two types is not feasible.
  • This kind of error commonly arises from incorrect assignment or initialization of function pointers or callbacks in your code.

 

Identify the Source of the Error

  • Examine your code for any place where a function pointer is assigned a potential integer value. Check the lines where functions are called, especially callbacks.
  • Look specifically at the locations where you are setting up function pointers or callback structures to identify if an integer is mistakenly being used.

 

Fix the Conversion Error

  • Verify whether the function pointer is assigned correctly. If you need to assign a specific function, ensure the syntax and function signature match the declaration correctly. For example:
  • void myFunction() {
        // function implementation
    }
    
    void (\*functionPointer)() = myFunction;  // Correct assignment
    
  • If the intention is to call a function that returns an int, ensure that the call is handled properly and the result is not mistakenly being used as a function pointer. If you receive an int, it should be stored or processed as such.
  • Sometimes error stems from conditional logic; ensure that function pointers are being set up correctly and not conditionally set to integer literals:
  • 
    void handleSetup(bool condition) {
        if (condition) {
            functionPointer = myFunction;  // Proper function assignment
        } else {
            functionPointer = nullptr;  // Use a null pointer when needed
        }
    }
    

 

Utilize Correct Type Casting

  • If assigning integers is unavoidable (in embedded systems sometimes hardware register addresses might be involved), you should handle it safely by using reinterpret\_cast for explicit type casting, while clearly understanding the implications of such a conversion.
  • 
    void (\*functionFromAddr)();
    int address = 0x1000;  // Example address
    functionFromAddr = reinterpret\_cast(address);  // Cast with care
    
  • Note: It is critical to ensure that such a cast is safe and justified by the context of application, considering the potential risks involved with reinterpret\_cast.

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