C 结构体中的未声明函数

Question

I have the following code :

#include <stdio.h>
#include <string.h>

void getData() {

    static int HasDataBeenWritten;

    if (HasDataBeenWritten == 0) {

        enum flags
        {
            Country_NA = 1, 
            CountryUS = 2,
            CountryCN = 4, 
            CountryCA = 8, 
            Business_NA = 16,
            BusinessYes = 32,
            BusinessNo = 64,
            TypeOfEntityNonCommericial = 128,
            EntityPersonal = 256,
            EntityAll = 512,
        };

        struct TopDomain
        { 
            char *DomainName;
            unsigned int DataFlags:9;
        };          

        static struct TopDomain DomainData[8];

        static char DomainNameArray1[3] = {"EDU"};
        DomainData[0].DomainName = DomainNameArray1;    
        DomainData[0].DataFlags = 145;
        HasDataBeenWritten = 1;
    }

    printf("DomainData[0] : %i", (DomainData[0].DomainName));
    printf("DomainData[0] : %d", DomainData[0].DataFlags);
}

I want to print the array that the *DomainName is pointing to or even just the pointer. However, I am getting this error message

getData.c:48:32 error: 'DomainData' undeclared (first use in this function) (printf("DomainData[0] : %i", (DomainData[0].DomainName));

Do I need to declare the struct within the array or what?

Answer 1

You need to declare DomainData (which is an array of struct TopDomain structures) in a place that's visible at the point of the printf call.

You've declared it inside a set of curly braces. The scope of the name extends from the declaration to the nearest enclosing } , which is just before the printf calls. (Since it's static , its lifetime is the entire execution of the program, so the object still exists at that point. The problem is that its name is not visible.)

Since DomainData depends on the declarations of struct TopDomain and enum flags , you'll need to move those as well.

(It rarely makes much sense to declare a type inside a compound statement.)

Incidentally, your format strings are incorrect. In your first printf , you use %i for an argument of type char* ; you want %s (assuming the pointer isn't NULL ). In your second you use %d for an argument of type unsigned int ; you want %u (or 0x%x might be clearer in this case).