Class differences between C++03 and C++11 - c++

Question

I'm current building an application in which I have a log function that is accessible in most of my classes which was declared as below:
FileHandler.h
#ifndef FILEHANDLER_H
#define FILEHANDLER_H
#pragma once
#include <SDL.h>
#include <string>
#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include <algorithm>
#include <cctype>
//Include to allow logging
#include "log.h"
class fileHandler
{
public:
fileHandler();
virtual ~fileHandler();
void WriteToFile(const std::string& filename, std::string textToWrite);
std::vector<std::string> ReadFromFile(const std::string& filename);
std::string& TrimString(std::string& stringToTrim);
protected:
private:
class log logHandler;
std::vector<std::string> blockOfText;
std::string currentLine;
};
#endif // FILEHANDLER_H
Log.h
#ifndef LOG_H
#define LOG_H
#pragma once
#include <SDL.h>
#include <string.h>
#include <iostream>
#include <sstream>
#include <fstream>
#include <time.h>
class log
{
public:
log();
virtual ~log();
void static WriteToConsole(std::string textToWrite);
void WriteToLogFile(std::string textToWrite);
protected:
private:
};
#endif // LOG_H
This worked fine for a long time and then I wanted to include another function elsewhere in my application that was only compatible with C++11 so I told the compiler to compile to these standards. I was then receiving an error on "log logHandler" saying log is not a declared name.
I was able to resolve the problem by changing the line to
class log logHandler;
I was wondering if anybody could tell me what has changed between C++03 and C++11 that required me to do this?
EDIT: Included all relevant code to make question more complete.

Answer 1

You don't show your real code (missing ; at the end of the class declaration, no #endif), but chances are that your problem is somehow related to std::log, which has received a new overload in C++11, in combination with a using namespace std somewhere in your code.
Note that the new overload is probably irrelevant to the problem at hand; the real reason may very well be a change somewhere in your compiler's standard-library implementation causing an internal #include <cmath>. This means that even in C++03, your code was only working by sheer coincidence, and a conforming C++03 compiler was always allowed to reject it.
Here is an example program which may reproduce your problem:
#include <cmath>
using namespace std;
struct log
{
};
int main()
{
// log l; // does not compile
struct log l; // compiles
}

Answer 2

Nothing has changed about how the code you posted is treated.
What I suspect is, that you somewhere have an
#include <cmath>
And below that, somewhere else
using namespace std;
This causes your compiler to not be able to unambiguously resolve the name log, since there is std::log (a function) and your class log.
By explicitly stating class log, you tell the compiler that you are referring to the class.