C++ compilation error: The return type of the function does not match the return type declared by the function. How to solve it?

In C programming, it is a common compilation error that the return type of a function does not match the return type of the function declaration. This error usually occurs because developers have some inconsistencies in the function declaration and definition process, such as function return type mismatch, parameter number or type mismatch, etc. These errors often cause the program to fail to compile or run correctly, causing considerable trouble in the development and maintenance of the program.

So, why does a compilation error occur if the return type of a function does not match the return type declared by the function? This is because the C compiler determines the return type of the function based on the function's declaration. If the return type of the function is inconsistent with the declared type, the compiler cannot determine the return type of the function, and a compilation error occurs. Therefore, in order to solve this error, we need to consider the following two aspects:

1. Check whether the return type in the function declaration and definition is consistent

When the function is declared If the return type is inconsistent with the definition, the compiler will throw an error. Therefore, when solving this kind of error, we first need to check whether the return type in the function declaration and definition is consistent. If it is inconsistent, we need to modify the return type in the function definition to make it the same as the return type in the declaration.

For example, in the following code, the return type of the function declaration is int, but the return type in the function definition is void, which will cause a compilation error:

// 函数声明
int add(int a, int b);

// 函数定义
void add(int a, int b) {
    int c = a + b;
    return c;
}

The correct function definition should be like this ：

int add(int a, int b) {
    int c = a + b;
    return c;
}

2. Check whether the return statement and return value type of the function are consistent

In addition to the return type mismatch, if the return statement and return value type of the function are inconsistent, The compiler will also throw errors. Therefore, when solving this error, we need to check whether the return statement and return value type of the function are consistent. If it is inconsistent, we need to modify the return statement or return value type to make it consistent.

For example, in the following code, the return value type of the function is int, but the return statement returns a value of type char, which will also cause a compilation error:

int get_value() {
    char ch = 'A';
    return ch;
}

Correct function The implementation should be like this:

int get_value() {
    int i = 10;
    return i;
}

To sum up, when we encounter a compilation error where the return type of a function does not match the return type of the function declaration, we first need to check whether the return types in the function declaration and definition are consistent. . If they are consistent but there are still errors, you need to check whether the return statement and return value type of the function are consistent. Only when both match, the compiler can correctly determine the return type of the function, so that the entire program can compile and run smoothly.

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