Trouble creating assert function

Question

This is my assert function (it wont compile "error C2110: '+' : cannot add two pointers"):

#define CHAR(x) #x

template<typename T>
inline void ASSERT(T x)
{
    if(!x)
    {
        std::string s("ERROR! Assert " + CHAR(x) + " failed. In file " + __FILE__ +
                      " at line " + __LINE__ + ".");
            std::wstring temp(s.length(), L' ');
            std::copy(s.begin(), s.end(), temp.begin());
            getLogger().Write(temp);
        }
    }

Any idea of how to fix it?

Note that you can't write this as a function; the use of __FILE__ and __LINE__ require that it is implemented as a macro (assuming you want the file and line in which the ASSERT is used). — James McNellis
– James McNellis, Commented Sep 15, 2011 at 22:49
Yes, even then. Inlining doesn't affect the output of a function. (If it does, your compiler is broken.) — Rob Kennedy
– Rob Kennedy, Commented Sep 15, 2011 at 23:01
@Tiago Costa: It needs to be a macro because __FILE__ and __LINE__ are preprocessor macros which will be "magically" replaced by constants later. — AJG85
– AJG85, Commented Sep 15, 2011 at 23:04
When you're writing C++, you should use std::string. Then this entire issue just disintegrates. (This means that each [sort of] string literal in your code should be wrapped in a temporary instantiation of std::string; then you can rely on std::string's op+ to do the heavy lifting for you.) In this case, as others have said, you can just rely on preprocessor concatenation, but this won't always be available to you. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Sep 15, 2011 at 23:28

Mooing Duck · Accepted Answer · 2011-09-15 23:54:22Z

2

String Literals are easily reduced to char pointers, which cannot be added as you try to do with "ERROR! Assert " + CHAR(x) + " failed. In file ".... However, C++ has the handy feature of doing this automatically before compilation! (the preprocessor does this). Even better, it has a handy tool for making wide strings at compile time. So, you want:

#define _T(x) L ## x
#define CHAR(x) #x
#define CHAR2(x) CHAR(x)
#define ASSERT(x) ASSERT2(x, CHAR(x), __FILE__, CHAR2(__LINE__))
#define ASSERT2(x, t, f, l) \
if(!x) \
    getLogger().Write(L"ERROR! Assert " _T(t) L" failed. In file " _T(f) L" at line " _T(l) L".");

http://ideone.com/0ibcj

edited Sep 15, 2011 at 23:54

answered Sep 15, 2011 at 22:56

Mooing Duck

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6 Comments

Tiago Costa Over a year ago

No compile errors. But #define CHAR(x) #x is not working correctly... Its outputting: "ERROR! Assert x failed. In file FILE at line LINE."

Mooing Duck Over a year ago

Are FILE and LINE displaying properly? Hard to tell from your comment. Also, did you make ASSERT into a macro or a function?

Tiago Costa Over a year ago

No they are not displayed properly... I turned ASSERT into a macro

Mooing Duck Over a year ago

What happens if you remove the CHAR() macro and put in just # then?

Tiago Costa Over a year ago

I've changed the code to this: ideone.com/gBceP. But I get 3 compile errors: error C2064: term does not evaluate to a function taking 1 arguments / error C2143: syntax error : missing ')' before 'string' / error C2059: syntax error : ')'

|

Lightness Races in Orbit · Accepted Answer · 2011-09-15 23:27:50Z

0

The compiler error is quite clear; you are trying to apply the + operator to string literals. A quick way to fix it is enclosing the first string literal in std::string().

As @James McNellis pointed out, note that FILE and LINE will point to the file and line of the assert function declaration.

edited Sep 15, 2011 at 23:27

Lightness Races in Orbit

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answered Sep 15, 2011 at 22:51

K-ballo

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Comments

Lightness Races in Orbit · Accepted Answer · 2011-09-15 23:28:13Z

0

You cannot use the + operator to concatenate two char*s; you need printf or some sort of thing for that.

edited Sep 15, 2011 at 23:28

Lightness Races in Orbit

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answered Sep 15, 2011 at 22:51

JRL

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Comments

Lightness Races in Orbit · Accepted Answer · 2011-09-15 23:28:26Z

0

"ERROR! Assert " is a null-terminated, C-style string. You can't execute operator+ on it.

edited Sep 15, 2011 at 23:28

Lightness Races in Orbit

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answered Sep 15, 2011 at 22:50

Igor

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1 Comment

Rob Kennedy Over a year ago

Sure you can. It just doesn't do what's desired here, and there are restrictions on what the other operand can be.

NuSkooler · Accepted Answer · 2011-09-16 14:52:24Z

0

A few issues:

Generally an assert should break into the debugger or dump if one is not attached. This will not.
As already mentioned, your LINE and FILE require use in a macro
You need a couple "helper" macros to get the strings working properly

Try something along these lines:

#define ASSERT_QUOTE_(x) #x
#define ASSERT_QUOTE_(x) ASSERT_QUOTE_(x)

#define MY_ASSERT(cond) \
  if(cond) {} else { \
    std::stringstream ss; \
    ss << "ERROR! Assert " << ASSERT_QUOTE(cond) << " failed. In file " << __FILE__ << " at line " << __LINE__ << "."; \
    getLogger().Write(ss.str()); \
  }

Be careful trying to use STL here however. I suggest you have your logger's Write() function take variable arguments and process them with printf() or perhaps boost::format

edited Sep 16, 2011 at 14:52

answered Sep 15, 2011 at 23:47

NuSkooler

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