使用预处理器 C++ 定义常见错误消息

Question

Let's say I have multiple places where I call function int foo(x, y) . Based on the return code, I decide whether to print an error message or not. So the code looks similar to this:

  void func1()
    {
        ...
        if(foo(x,y))
            std::cerr << "Error occurred with values" << x << "," << y << __LINE__;
        ...
    }

    void func2()
    {
        ...
        if(foo(x,y))
            std::cerr << "Error occurred with values" << x << "," << y << __LINE__;
        ...
    }

The problem that I have is that "Error occurred" is repeating in many places and is the same everywhere. I was wondering if it's a good practice to define common error messages using #define and reuse them. So the code would like like this:

  #define errMsg(x,y) \
    std::string("Error occurred with values " + to_string(x) + "," + to_string(y) + to_string(__LINE__))

  void func1()
    {
        ...
        if(foo(x,y))
            std::cerr << errMsg;
        ...
    }

    void func2()
    {
        ...
        if(foo(x,y))
            std::cerr << errMsg;
        ...
    }

Answer 1

The obvious thing to do is just to put the error message in foo itself. If you can't do that, then just wrap it:

bool fooWithLogging(int x, iny y)
{
    auto result = foo(x,y);
    if (result)
    {
        std::cerr << "Error occurred with values" << x << "," << y << std::endl;
    }
}

The call the wrapper in your code:

void func1()
{
    ...
    fooWithLogging(x,y);
    ...
}

void func2()
{
    ...
    fooWithLogging(x,y);
    ...
}

Bonus: make the logging dynamic:

#ifdef DEBUG
bool g_isFooLoggingEnabled = true;
#else
bool g_isFooLoggingEnabled = false;
#endif

bool fooWithLogging(int x, iny y)
{
    auto result = foo(x,y);
    if (result && g_isFooLoggingEnabled)
    {
        std::cerr << "Error occurred with values" << x << "," << y << std::endl;
    }
}

And now with your FILE and LINE requirement that just alluded to in the comments:

bool _fooWithLogging(int x, iny y, const std::string& filename, int line)
{
    auto result = foo(x,y);
    if (result && g_isFooLoggingEnabled)
    {
        std::cerr << "Error occurred in file" << filename << " on line " << line << " with values" << x << "," << y << std::endl;
    }
}

#define FooWithLogging(x, y) _fooWithLogging(x, y, __FILE__, __LINE__)

Then in code:

void func1()
{
    ...
    FooWithLogging(x,y);
    ...
}