gcc arm error: '::fileno' has not been declared

Question

I'm trying to get spdlog to work with on my embedded project. (Yes I know spdlog is not designed for embedded projects, but I'd like to give it a try ;))

I already managed to forward c++ std::thread, std::mutex etc to proper FreeRTOS Objects. So this is not an issue any more.

The actual code is pretty simple. The data should be written to a log file. Theactual file writing should be done via embedded FATFS Library

#include <spdlog/logger.h>

void foo()
{
  // create a file rotating logger with 5mb size max and 3 rotated files
  auto file_logger = spdlog::rotating_logger_mt("file_logger", "myfilename", 1024 * 1024 * 5, 3);
}

However this results in a compiler error

../User/ThirdParty/spdlog/details/os-inl.h: In function 'size_t spdlog::details::os::filesize(FILE*)':
../User/ThirdParty/spdlog/details/os-inl.h:231:16: error: '::fileno' has not been declared
  231 |     int fd = ::fileno(f);
      |                ^~~~~~
../User/ThirdParty/spdlog/details/os-inl.h: In function 'bool spdlog::details::os::in_terminal(FILE*)':
../User/ThirdParty/spdlog/details/os-inl.h:432:21: error: 'fileno' was not declared in this scope; did you mean 'file'?
  432 |     return ::isatty(fileno(file)) != 0;
      |                     ^~~~~~
      |                     file

Now i already have a wrapper for the syscalls

int _open(char *path, int flags, ...)
{
    /* Pretend like we always fail */
    return -1;
}

int _close(int file)
{
    return -1;
}


__attribute__((weak)) int _read(int file, char *ptr, int len)
{
    
return -1;
}

__attribute__((weak)) int _write(int file, char *ptr, int len)
{
    return -1;
}

Why am i still getting the error? Do i have to add

--wrap=_read
--wrap=_write

etc. to the linker flags?

Could you help me out here?

Answer 1

This is a compiler error not a linker error. I added a declaration of

int fileno(FILE *stream)
{
    errno = ENOENT;
    return -1;
}

before the spdlog include. This solved the issue

Unfortunately spdlog does not support a bare metal plattform right now :O

Line 231:

// OpenBSD doesn't compile with :: before the fileno(..)

#if defined(__OpenBSD__)
    int fd = fileno(f);
#else
    int fd = ::fileno(f);
#endif