Question

I have one C++ define statement as:

#define PING 10

In my main function, I have something like:

int main()
{
    int code;
    cout<<"enter command code";
    cin>>code;      // value entered 10
    cout<<code;   //here i want "PING" output instead of 10
                
    return 0;
}

How can I replace 10 with PING in my output?

Edit:

i will have multiple #define as

#define PING 10
#define STATUS 20
#define FETCH 74
#define ACK 12
#define TRAIL 9
#define EXIT 198

now my bussiness logic will get only command code i.e 10 or 12 etc etc

i want to retreive corresponding command name for that code..how is it possible??

Answer 1

How about replacing:

cout << code;

with:

if (code == PING)
    cout << "PING";
else
    cout << code;

That’s the easiest way if you have a single #define. For more complicated cases, you could have an array of strings to look up, based on the #define values, something like:

#define E_OK        0
#define E_NOMEM     1
#define E_BADFILE   2
#define E_USERERROR 3
#define E_NEXT_ERR  4

static const char *errStr[] = {
    "Okay",
    "No memory left",
    "Bad file descriptor",
    "User is insane",
};
:
if ((errCode < 0) || (errCode >= E_NEXT_ERR))
    cout << "Unknown error: " << errCode << '\n';
else
    cout << "Error: " << errStr[errCode] << '\n';

If the values are disparate, you can opt for a non-array-based solution, such as:

#define PING 10
#define STATUS 20
#define FETCH 74
#define ACK 12
#define TRAIL 9
#define EXIT 198
:
const char *toText (int errCode) {
    if (errCode == PING  ) return "Ping";
    if (errCode == STATUS) return "Status";
    if (errCode == FETCH ) return "Fetch";
    if (errCode == ACK   ) return "Ack";
    if (errCode == TRAIL ) return "Trail";
    if (errCode == EXIT  ) return "Exit";
                           return "No idea!";
}

---

The other thing you may want to consider doing is replacing #define values with enumerated constants. It may not matter for simple things like this but the type safety and extra information provided will almost certainly ease your debugging efforts at some point in your career.

Nowadays, I generally only use #define for conditional compilation. Constants are better done with enumerations and it’s been a long time since I could out-think compilers on what should and shouldn’t be an inline function 🙂