#Expressing variable sized const char* array using std::array

20 messages · Page 1 of 1 (latest)

sudden ether
#

Hi, I have the following the following piece of code:

    const char* known_extensions[] = {
      ".mia",
      ".mib",
      ".mic",
#ifdef TIFF_SUPPORT
      ".tiff",
      ".tif",
      ".TIFF",
      ".TIF",
#endif
#ifdef PNG_SUPPORT
      ".png",
      ".PNG",
#endif
      nullptr
    };

Is there a way to express this using std::array ? I'd like an easy to way to evaluate the size of the array depending on whether those macros are actually defined.

upbeat lintelBOT
#

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tired flame
#

;compile

#include <array>
    std::array known_extensions {
      ".mia",
      ".mib",
      ".mic",
#ifdef TIFF_SUPPORT
      ".tiff",
      ".tif",
      ".TIFF",
      ".TIF",
#endif
#ifdef PNG_SUPPORT
      ".png",
      ".PNG",
#endif
    };

int main(){}
steady obsidianBOT
#
Compilation successful

No output.

ZeroPointer#6105 | 108ms | c++ | x86-64 gcc 13.1 | godbolt.org
tired flame
#

There we go

sudden ether
#

Ah ok nice. Didn't know that you could get away without specifying size

tired flame
#

In c++17 and onward, you don't have to specify template argument if they can be inferred from the constructor arguments

sudden ether
#

Brilliant!

sudden ether
#

Is there a way to determine the type induced by the compiler though? Ideally I would like the array above to be a std::arraystd::string

tired flame
#

Hmmm, that one might be more tough

sudden ether
#

I guess the easiest way would be to just wrap the strings with std::string

tired flame
#

;compile

#include <array>
#include <string>

using namespace std::string_literals;

    std::array known_extensions {
      ".mia"s,
      ".mib"s,
      ".mic"s,
#ifdef TIFF_SUPPORT
      ".tiff"s,
      ".tif"s,
      ".TIFF"s,
      ".TIF"s,
#endif
#ifdef PNG_SUPPORT
      ".png"s,
      ".PNG"s,
#endif
    };

int main(){}
steady obsidianBOT
#
Compilation successful

No output.

ZeroPointer#6105 | 57ms | c++ | x86-64 gcc 13.1 | godbolt.org
tired flame
#

I prefer using the string literal namespace here

sudden ether
#

Yes, I guess that's a little nicer.

kind falcon
#

you can also ensure that the inferred type is correct using type traits:

#

;compile --std=c++20

#include <array>
#include <string>
#include <type_traits>

using namespace std::string_literals;

    std::array known_extensions {
      ".mia"s,
      ".mib"s,
      ".mic"s,
#ifdef TIFF_SUPPORT
      ".tiff"s,
      ".tif"s,
      ".TIFF"s,
      ".TIF"s,
#endif
#ifdef PNG_SUPPORT
      ".png"s,
      ".PNG"s,
#endif
    };

static_assert(std::is_same_v<decltype(known_extensions)::value_type, std::string>);

int main(){}
steady obsidianBOT
#
Compilation successful

No output.

Raldryniorth the Dragon#3621 | 63ms | c++ | x86-64 gcc 13.1 | godbolt.org
kind falcon
#

(if you want to be sure it does the thing you want it to do

sudden ether
#

!solved