C++ compilation error: The compiler does not support multiple definitions with different types. How to solve it?

When writing programs in C, we may encounter compilation errors. One of the common errors is "The compiler does not support multiple definitions of different types." This error usually involves multiple variables or functions being defined in different files or in different locations in the same file, and their types do not match, causing the compiler to be unable to determine which definition to use. This article will explain the cause and solution of this error.

1. Cause of the error

In C, variables or functions can be defined in different files or in different locations in the same file. When multiple definitions are present, the compiler must determine which one to use. If multiple definitions have different types, the compiler cannot determine which definition to use and will report an error.

For example, a variable named x and a function named y are defined in a program:

// file1.cpp
int x = 1;

// file2.cpp
double y() { return 2.0; }

In this example, the type of x is int, and the type of y is double. During compilation, if file1.cpp and file2.cpp are included at the same time, the compiler will report an error "The compiler does not support multiple definitions with different types".

2. Solution

In order to solve this problem, we need to use the extern keyword to declare these variables or functions so that they can be used in other files.

In file1.cpp, you need to declare the y function using extern so that the compiler knows that the y function is defined in another file and can correctly parse the return type of the y function. Similarly, in file2.cpp, the x variable needs to be declared using extern. The modified code looks like this:

// file1.cpp
extern double y();

int x = 1;

// file2.cpp
extern int x;

double y() { return 2.0; }

In this example, the extern keyword is used to tell the compiler that these variables or functions are defined in other files. In this way, at compile time, the compiler can correctly resolve their types, thus avoiding the error "The compiler does not support multiple definitions with different types".

3. Summary

In C, when multiple definitions appear, if the defined types are different, the compiler will report "The compiler does not support multiple definitions with different types." "mistake. To solve this problem, we need to declare these variables or functions using extern keyword so that we can use them in other files. This way, at compile time, the compiler can correctly resolve their types, thus avoiding errors.

The above is the detailed content of C++ compilation error: The compiler does not support multiple definitions with different types. How to solve it?. For more information, please follow other related articles on the PHP Chinese website!