C++ macro with argument

Question

I want to define like this:

    #define log(x)          \
    #if (x)                 \
        cout << "\n" << x   \
    #else                   \  
        cout                \

Example:

    log() << abc 
    ~
    cout << abc

and

    log(name) << abc
    ~
    cout << "\n" << name << abc

It similar the problem in the question in here C preprocessor macro specialisation based on an argument

I want to use define because actually, I use cout for people can easily understand my intent.

I doing the Qt and need log using QLoggingCategory

    QLoggingCategory category("MyNameSpace");

And when need log, I need to use the syntax

    qCDebug(category) << something_need_log

Here, qCDebug(category) like the cout in my question.

Sorry, macros don't work this way, and this is not what they're for. This is something that easily done using a very simple template function. — Sam Varshavchik
– Sam Varshavchik, Commented Aug 22, 2019 at 2:12
Why do you want to use a macro? They tend to cause more problems than the alternatives. (By which I mean they cause problems and the alternatives usually do not.) — JaMiT
– JaMiT, Commented Aug 22, 2019 at 2:15
Macros, old style cast, most implicit conversions, etc. are things that C++ has only because deprecating them just breaks to much code, but they should be avoided in new code. — Mirko
– Mirko, Commented Aug 22, 2019 at 3:50

3CEZVQ · Accepted Answer · 2019-08-22 03:19:42Z

2

#include <iostream>

std::ostream& log() {
  return std::cout;
}

std::ostream& log(const std::string& x) {
  return std::cout << "\n" << x;
}

int main() {
    log() << "message";  // std::cout << "message";
    log("name: ") << "message"; // cout << "\n" << "name: " << message;
    return 0;
}

Output:

message
name: message

edited Aug 22, 2019 at 3:19

answered Aug 22, 2019 at 2:23

3CEZVQ

43k11 gold badges92 silver badges100 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

tackelua Over a year ago

Thanks @S.M. but I want to use define because actually, I use cout for people can easily understand my intent. I doing the Qt and need log using QLoggingCategory QLoggingCategory category("MyNameSpace"); And when need log, I need to use the syntax qCDebug(LogQuoteButton) << something_need_log Here, qCDebug(LogQuoteButton) like the cout in my question.

Collectives™ on Stack Overflow

C++ macro with argument

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related