Convert from #define to string c++

Question

I would like to convert from #define to string.

My code:

#ifdef WIN32
#define PREFIX_PATH = "..\\"
#else
#define PREFIX_PATH = "..\\..\\"
#endif


#define VAL(str) #str
#define TOSTRING(str) VAL(str)

string prefix = TOSTRING(PREFIX_PATH);
string path = prefix + "Test\\Input\input.txt";

But, it didn't work..

prefix value is "..\\\"

Any idea what is the problem..

Thanks!

PREFIX_PATH is already defined as a quoted string, but it is passed through VAL, which tries to quote the symbol again, with #. Also, note that non-Windows OS's usually use forward slashes, not backslashes as a path separator. — Christopher Oicles
– Christopher Oicles, Commented Oct 25, 2016 at 10:31

user31264 · Accepted Answer · 2016-10-25 10:43:45Z

7

You don't need "=" in defines, or any #str, or "+" between double quoted strings.

#ifdef WIN32
    #define PREFIX_PATH "..\\"
#else
    #define PREFIX_PATH "..\\..\\"
#endif

string path = PREFIX_PATH "Test\\Input\\input.txt";

answered Oct 25, 2016 at 10:43

user31264

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Mr.C64 · Accepted Answer · 2016-10-25 10:42:51Z

7

What about something simpler like that?

#ifdef WIN32
const std::string prefixPath = "..\\";
#else
const std::string prefixPath = "..\\..\\";
#endif

std::string path = prefixPath + "Test\\Input\\input.txt";

PS You may have a typo in the last line, in which you may miss another \ before input.txt.

As an alternative, if your C++ compiler supports this C++11 feature, you may want to use raw string literals, so you can have unescaped \, e.g.:

std::string path = prefixPath + R"(Test\Input\input.txt)";

edited Oct 25, 2016 at 10:42

answered Oct 25, 2016 at 10:27

Mr.C64

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2 Comments

Lightness Races in Orbit Over a year ago

"which I almost copied-and-pasted from your question" Almost? That's exactly what you've done :P

Mr.C64 Over a year ago

@LightnessRacesinOrbit: Not exactly, note the prefixPath instead of just prefix :)

James Elderfield · Accepted Answer · 2016-10-25 10:35:52Z

2

Although I'd highly recommend Mr.C64's approach, but if you want to use define for some reason then,

#ifdef WIN32
    #define PREFIX_PATH "..\\"
#else
    #define PREFIX_PATH "..\\..\\"
#endif

std::string prefix = PREFIX_PATH;
std::string path = PREFIX_PATH + "Test\\Input\\input.txt";

For #define you don't put an equals between key and value, and the TOSTRING function was unnecessary. #define is just find-replace so thinking in those terms might help you use it.

answered Oct 25, 2016 at 10:35

James Elderfield

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