Writing to file using overloaded operator << - problem with recursion

user_16003364 0
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I´m currently learning C++ and I decided to try to write my own "log tool". My goal is, that I can write just something like this:

logger<<"log message";

I have this problem - when I wrote operator << overloading function, the IDE compiler warned me, that it is infinite recursion.

Here is the code of operator overloading:

Logger &operator<<(Logger &logger, char *message)
{

logger << message << "Log message";

return logger;
}

And function is in class declared as friend:

friend Logger &operator<<(Logger &logger, char *message);

Why is this code infinite recursion? Maybe I just can´t see some trivial mistake...

Thank you for your answers.

c++
2 Answers
Logger &operator<<(Logger &logger, char *message)

This declares an operator<< overload. It takes a left-hand side parameter that's a Logger &, and a right-hand side parameter that's a char *, that's what this means in C++.

logger << message

And this invokes the << operator. Amongst all the defined operator overloads for <<, there is one operator overload that will work here: this particular operator overload takes a left-hand side parameter that's a Logger & -- and this logger object meets this criteria smashingly well -- and a right-hand side parameter that's a char * -- that's equally met well by the message object.

In other words, this calls the same operator<< overload, hence the infinite recursion.

user_39433120

In order to invoke your overloaded operator<< from anywhere, you need a Logger object on the left side and a char* pointer (BTW, it should be const char* instead) on the right side.

Inside your overloaded operator<<, this statement:

logger << message

is trying to invoke an operator<< with a Logger object on the left side and a char* pointer on the right side.

So, what do you think that is going to invoke? That's right, ITSELF! Over and over, endlessly, forever. That is what the compiler is warning you about.

You need to replace logger in that statement with whatever std::istream (or other object) that the Logger class wants to write to. Not the Logger itself.

For example, let's say your Logger class has a data member named m_file. Your overloaded operator<< could then look like this:

Logger& operator<<(Logger &logger, const char *message)
{
    logger.m_file << message << "Log message";
    return logger;
}
user_658630
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