error: 'fmt' has not been declared

[YanzhaoW]

Hi,

I'm using this library downloaded from Conan center, which use cista.h single header file.

I got an error with a hello world example:

#include "cista.h"
#include <iostream>
int main() {
   std::cout << "Hello world\n";
}

The error is:

/u/land/software/gcc/latest/bin/g++ -DASIO_STANDALONE -isystem /u/yanwang/.conan2/p/asio70e8791ea9016/p/include -isystem /u/yanwang/.conan2/p/b/fmtc97181cbd62d9/p/include -isystem /u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include -m64 -O3 -DNDEBUG -std=gnu++17 -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c /u/yanwang/test/cpp/asio/main.cpp
In file included from /u/yanwang/test/cpp/asio/main.cpp:4:
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:541:8: error: ‘fmt’ has not been declared
  541 | struct fmt::formatter<cista::bitset<Size>> : ostream_formatter {};
      |        ^~~
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:541:22: error: expected unqualified-id before ‘<’ token
  541 | struct fmt::formatter<cista::bitset<Size>> : ostream_formatter {};
      |                      ^
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:815:8: error: ‘fmt’ has not been declared
  815 | struct fmt::formatter<cista::strong<T, Tag>> : ostream_formatter {};
      |        ^~~
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:815:22: error: expected unqualified-id before ‘<’ token
  815 | struct fmt::formatter<cista::strong<T, Tag>> : ostream_formatter {};
      |                      ^
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:4755:8: error: ‘fmt’ has not been declared
 4755 | struct fmt::formatter<cista::basic_string<Ptr>> : ostream_formatter {};
      |        ^~~
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:4755:22: error: expected unqualified-id before ‘<’ token
 4755 | struct fmt::formatter<cista::basic_string<Ptr>> : ostream_formatter {};
      |                      ^
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:9080:8: error: ‘fmt’ has not been declared
 9080 | struct fmt::formatter<cista::indexed<T>> : ostream_formatter {};
      |        ^~~
/u/yanwang/.conan2/p/cista8c77ed80eecd5/p/include/cista.h:9080:22: error: expected unqualified-id before ‘<’ token
 9080 | struct fmt::formatter<cista::indexed<T>> : ostream_formatter {};

I digged into the header file and it's caused by

#if __has_include("fmt/ostream.h")

template <typename T, typename Tag>
struct fmt::formatter<cista::strong<T, Tag>> : ostream_formatter {};

#endif

I think __has_include just means whether the header file is capable to be included, instead of whether the library has been already included.

[felixguendling]

You're right. My mistake. Can you please create a PR that adds the #include statement?

[YanzhaoW]

Hi,

Sorry I'm not familiar with the program structure of this project and have no idea how cista.h is stitched together. So I think it's better to have someone who already had some experience add the #include statement. :D

[zhoupengwei]

@YanzhaoW It depends on the fmt ostream. Please include the fmt ostream header before using cista, as shown in the following example:

#include <fmt/ostream.h>
#include "cista.h"

[felixguendling]

The idea was that it does not depend on libfmt but it is compatible if libfmt is available. So it was my mistake to only check for the include but not actually include it. @zhoupengwei your work around won't be necessary anymore after this is fixed. I just didn't find the time to add the #include statements after the __has_include checks.

[geniusdo]

I added #include <fmt/ostream.h> before including cista.h. Still can't get it compiled. Is it gonna be fixed at any time

[felixguendling]

You can just remove fmt completely or have a version that has ostream_formatter. Then it works.

[felixguendling]

Maybe additionally a version check is required.

[geniusdo]

I think it would be nice if use fmt or not can be a compile option. I tried to regenerate the header file from source, failed again cuz of fmtlib.

[felixguendling]

I added a CISTA_FMT flag.