I'm writing a C project and I want to test it using catch2 framework. But I'm having some odd behaviors with a function that returns a struct.

The C code is bellow:

stream_type.h

#ifndef STREAM_TYPE
#define STREAM_TYPE

#include <stdint.h>

#ifdef __cplusplus
extern "C"
{
#endif

typedef struct StreamType
{
    size_t offset;
    const size_t size;
} StreamType;

StreamType stream_type_make(size_t size);

#ifdef __cplusplus
}
#endif

#endif // STREAM_TYPE

stream_type.c

#include "stream/stream_type.h"

StreamType stream_type_make(size_t size)
{
    return (StreamType){.size = size, .offset = 0};
}

My catch2 test:

stream_type_test.cpp

#include "catch.hpp"

#include "stream/stream_type.h"

#include <iostream>

TEST_CASE("stream_type_make must creat StreamType correctly",
          "[stream_type_make]")
{
    StreamType stream_made = stream_type_make(35);

    std::printf("offset: %X \n size: %X\n\n", stream_made.offset, stream_made.size);
}

Ps.: The imported file "catch2.hpp" is the file distributed in the v2.13.8

The output after build is:

[1/1] Cleaning all built files...
Cleaning... 14 files.
[8/14] Building CXX object test\CMakeFiles\GALI_utils_test.dir\src\utils_test.cpp.obj
C:\Users\ggabr\Desktop\utils\include\stream/stream_type.h(18): warning C4190: 'stream_type_make' has C-linkage specified, but returns UDT 'StreamType' which is incompatible with C
C:\Users\ggabr\Desktop\utils\include\stream/stream_type.h(12): note: see declaration of 'StreamType'
[12/14] Building CXX object test\CMakeFiles\GALI_utils_test.dir\src\stream\stream_type_test.cpp.obj
C:\Users\ggabr\Desktop\utils\include\stream/stream_type.h(18): warning C4190: 'stream_type_make' has C-linkage specified, but returns UDT 'StreamType' which is incompatible with C
C:\Users\ggabr\Desktop\utils\include\stream/stream_type.h(12): note: see declaration of 'StreamType'
[14/14] Linking CXX executable test\GALI_utils_test.exe

The output after run executable is:

[1/1] cmd.exe /C "cd /D C:\Users\ggabr\Desktop\utils\build\win-dbg\test && C:\Users\ggabr\Desktop\utils\build\win-dbg\test\GALI_utils_test.exe"

offset: CCCCCCCC 
size: CCCCCCCC

===============================================================================
test cases: 1 | 1 passed
assertions: - none -

Ps.: If necessary I can add the cmake files to, but my executable test target has the "cxx_std_20" compile feature.

So, why this is happen? Why the the "stream_made" variable is not initialized as expected (size = 35, offset = 0)?