Accessing External Variables in C

In C language, you can call an external variable by using the extern keyword to declare it. The specific steps are as follows:

1. Declare the variable in the source file where the external variable is located using the keyword extern, for example:

extern int externalVariable; // 声明外部变量externalVariable

1. In the source file where external variables are needed, simply use the external variables without declaring them again. For example:

#include <stdio.h>

extern int externalVariable; // 声明外部变量externalVariable

int main() {
    printf("External variable value: %d\n", externalVariable);
    return 0;
}

1. Simply compile and link the source file containing the external variable definitions together at linking time.

It is important to note that the definition of external variables can only appear in one source file, otherwise it will cause a duplicate definition error.