Given the following example:

#include "spdlog/spdlog.h"
#include "spdlog/sinks/stdout_sinks.h"
#include "spdlog/sinks/stdout_color_sinks.h"

int main()
{
    std::shared_ptr<spdlog::logger> logger1 = spdlog::stdout_logger_st("one");
    logger1->set_pattern("%v");
    logger1->info("hello");

    std::shared_ptr<spdlog::logger> logger2 = spdlog::stdout_color_st("two");
    logger2->set_pattern("%v");
    logger2->info("world");

    return 0;
}

If we run this program on Windows and redirect the output to a file (example.exe > output.txt) and have a look at this output in a hex editor, we see the following:

68 65 6C 6C 6F 0D 0D 0A 77 6F 72 6C 64 0D 0A
h  e  l  l  o  \r \r \n w  o  r  l  d  \r \n

i.e. "hello\r\r\nworld\r\n" - notice the additional carriage return after "hello".

I believe the first example can be explained because:

1. stdout_logger_st uses fwrite to write to the stdout handle
2. The formatter automatically appends \r\n by default
3. stdout is opened in text mode according to: https://docs.microsoft.com/en-us/cpp/c-runtime-library/text-and-binary-mode-file-i-o ("The stdin, stdout, and stderr streams always open in text mode by default")
4. Streams opened in text mode will automatically replace \n with \r\n according to: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/fwrite ("If stream is opened in text mode, each line feed is replaced with a carriage return-line feed pair")

This is a problem because some programs interpret the \r\r\n as two lines, resulting in all of the logs appearing with extra blank lines between them.

The only thing I can't explain is why the problem doesn't seem to happen with the color sink, which you can see from the output above produces the correct "world\r\n".