Returning a string from static function - c++

Question

I have two files: DateTime.h and DateTime.cpp which are shown below:
DateTime.h
class DateTime
{
public:
static string getCurrentTimeStamp();
};
DateTime.cpp
#include "stdafx.h"
#include "DateTime.h"
#include <ctime>
#include <chrono>
#include <iostream>
#include <string>
using namespace std;
string DateTime::getCurrentTimeStamp()
{
return "";
}
My compiler (Visual Studio 2012) is spitting out errors the moment I have the function getCurrentTimeStamp() return an std::string object. The errors all point to syntactic problems but none are clear. Does anyone understand why this may be the case?
Update: Here are (some of) the errors.
Error 6 error C2064: term does not evaluate to a function taking 0
arguments c:\users\anthony\documents\code\consoleapplication1\datetime.cpp 21 1 ConsoleApplication1
Error 1 error C2146: syntax error : missing ';' before identifier
'getCurrentTimeStamp' c:\users\anthony\documents\code\consoleapplication1\datetime.h 5 1 ConsoleApplication1
Error 7 error C2146: syntax error : missing ';' before identifier
'getCurrentTimeStamp' c:\users\anthony\documents\code\consoleapplication1\datetime.h 5 1 ConsoleApplication1
Error 5 error C2371: 'DateTime::getCurrentTimeStamp' : redefinition;
different basic
types c:\users\anthony\documents\code\consoleapplication1\datetime.cpp 10 1 ConsoleApplication1

Answer 1

When trying to diagnose an issue with a header file, especially a simple one like this, step 1 is to try and see what the compiler sees.
#include is a pre-processor directive, so the compiler doesn't see it, instead the compiler sees the pre-processed output of the file that you're trying to include.
So your code would look something like this:
#include "stdafx.h"
//#include "DateTime.h"
class DateTime
{
public:
static string getCurrentTimeStamp();
};
//#include "DateTime.h"
#include <ctime>
#include <chrono>
#include <iostream>
#include <string>
using namespace std;
string DateTime::getCurrentTimeStamp()
{
return "";
}
http://rextester.com/MODV66772
When I try and compile this on RexTester's online Visual Studio, I get very different errors, telling me that your stdafx.h isn't empty.
If I modify the code a little:
//#include "stdafx.h"
//#include "DateTime.h"
#include <string>
class DateTime
{
public:
static std::string getCurrentTimeStamp();
};
//#include "DateTime.h"
#include <ctime>
#include <chrono>
#include <iostream>
#include <string>
using namespace std;
string DateTime::getCurrentTimeStamp()
{
return "";
}
This now compiles without the errors/warnings you are reporting: http://rextester.com/PXE62490
The changes:
include in the header file, since the header depends on it,
use std::string instead of string,
The C++ compiler is a single-pass compiler, so the header file can't know that you are intending to do using namespace std later, and even if it did, it's a terrible practice because the std namespace is densely populated.
If you absolutely can't do with typing std:: all over the place, try using the names you need, e.g.
using std::string; // string no-longer needs to be std::string