Build errors with clang because of -Werror

[hephil]

Hi,

I noticed that this project sets -Werror when using Clang, which can cause build errors. I understand that the intended usage is to include the header and define your own tinyexr.cc, but since the repository also includes a CMake target (which compiles its own tinyexr.cc), it's easy to assume that linking against it is a supported use-case.

However, because -Werror is enforced internally, any outside project will break when compiling with clang.

If you don’t consider linking against the built-in target a valid use-case, feel free to close this.

Describe the issue
Project sets overly strict compiler flags for clang compiler which causes build errors when compiling the project with clang or when linking against the exposed cmake target.

The culprit is Line 44 following in CMakeLists.txt:

# Increase warning level for clang.
if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT MSVC)
  set(CLANG_COMPILE_FLAGS "-Weverything -Werror -Wno-padded -Wno-c++98-compat-pedantic -Wno-documentation -Wno-unused-member-function")
  if (${CMAKE_CXX_COMPILER_VERSION} VERSION_GREATER 16)
    set(CLANG_COMPILE_FLAGS "${CLANG_COMPILE_FLAGS} -Wno-unsafe-buffer-usage")
  endif()
  set_source_files_properties(${TINYEXR_SOURCES} PROPERTIES COMPILE_FLAGS ${CLANG_COMPILE_FLAGS})
endif ()

To Reproduce
Simple way:

1. Clone repo
2. Configure with cmake and clang as compiler (I used Clang 20.1.6 x86_64-pc-windows-msvc)
3. Observe build warnings in tinyexr.h (included by tinyexr.cc) regarding -Wununsed-macros and more promoted to errors because of -Werror

Complicated way:

1. Setup a project with the tinyexr repo in a subdirectory and link against :

project (project LANGUAGES CXX)
add_executable(dummy main.cc)
add_subdirectoy(tinyexr)
target_link_libraries(dummy PUBLIC tinyexr)

2. Compile the project with clang and observe above mentioned errors

Expected behavior
The project should not enforce -Werror on clang, provide an option to reliably disable -Werror from outside the project or fix the errors produced by -Werror.

Environment

• OS: Windows 11
• Compiler: Clang 20.1.6 x86_64-pc-windows-msvc

In the following is a minimal and naive way to fix the current warnings in tinyexr.h:

diff --git a/tinyexr.h b/tinyexr.h
index 37ca5b4..b1da5ba 100644
--- a/tinyexr.h
+++ b/tinyexr.h
@@ -89,6 +89,11 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 extern "C" {
 #endif
 
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-macros"
+#endif
+
 #if defined(_M_IX86) || defined(_M_X64) || defined(__i386__) || \
     defined(__i386) || defined(__i486__) || defined(__i486) ||  \
     defined(i386) || defined(__ia64__) || defined(__x86_64__)
@@ -225,6 +230,10 @@ extern "C" {
 #define TINYEXR_TILE_ROUND_DOWN (0)
 #define TINYEXR_TILE_ROUND_UP (1)
 
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 typedef struct TEXRVersion {
   int version;    // this must be 2
   // tile format image;
@@ -651,7 +660,7 @@ extern int LoadEXRFromMemory(float **out_rgba, int *width, int *height,
 #ifndef NOMINMAX
 #define NOMINMAX
 #endif
-#include <windows.h>  // for UTF-8 and memory-mapping
+#include <Windows.h>  // for UTF-8 and memory-mapping
 
 #if !defined(WINAPI_FAMILY) || (WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP)
 #define TINYEXR_USE_WIN32_MMAP (1)
@@ -4421,11 +4430,11 @@ static unsigned char **AllocateImage(int num_channels,
 
 #ifdef _WIN32
 static inline std::wstring UTF8ToWchar(const std::string &str) {
-  int wstr_size =
-      MultiByteToWideChar(CP_UTF8, 0, str.data(), (int)str.size(), NULL, 0);
-  std::wstring wstr(wstr_size, 0);
-  MultiByteToWideChar(CP_UTF8, 0, str.data(), (int)str.size(), &wstr[0],
-                      (int)wstr.size());
+  int wstr_size = MultiByteToWideChar(CP_UTF8, 0, str.data(),
+                                      static_cast<int>(str.size()), NULL, 0);
+  std::wstring wstr(static_cast<size_t>(wstr_size), 0);
+  MultiByteToWideChar(CP_UTF8, 0, str.data(), static_cast<int>(str.size()),
+                      &wstr[0], static_cast<int>(wstr.size()));
   return wstr;
 }
 #endif
@@ -6857,6 +6866,10 @@ struct MemoryMappedFile {
     }
 
     LARGE_INTEGER windows_file_size = {};
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wtautological-type-limit-compare"
+#endif
     if (!GetFileSizeEx(windows_file, &windows_file_size) ||
         static_cast<ULONGLONG>(windows_file_size.QuadPart) >
             std::numeric_limits<size_t>::max()) {
@@ -6864,6 +6877,9 @@ struct MemoryMappedFile {
       data = NULL;
       return;
     }
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
     size = static_cast<size_t>(windows_file_size.QuadPart);
 #elif defined(TINYEXR_USE_POSIX_MMAP)
     posix_descriptor = open(filename, O_RDONLY);

Have a nice day!

hephil

[syoyo]

Copilot says:

I'll help you understand this GitHub issue. Let me retrieve the details for you.This issue (#227) in the tinyexr repository reports a build problem with Clang due to overly strict compiler flags. Here's a breakdown:

Issue Summary

Title: Build errors with clang because of -Werror
Reporter: hephil
Created: 29 minutes ago
Status: Open

Problem Description

The issue occurs because the project's CMakeLists.txt sets -Werror (treat warnings as errors) specifically for Clang compilers. This causes builds to fail when:

1. Compiling the project directly with Clang
2. Linking against the CMake target from another project

Root Cause

The problematic code is in CMakeLists.txt at line 44:

# Increase warning level for clang.
if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT MSVC)
  set(CLANG_COMPILE_FLAGS "-Weverything -Werror -Wno-padded -Wno-c++98-compat-pedantic -Wno-documentation -Wno-unused-member-function")
  if (${CMAKE_CXX_COMPILER_VERSION} VERSION_GREATER 16)
    set(CLANG_COMPILE_FLAGS "${CLANG_COMPILE_FLAGS} -Wno-unsafe-buffer-usage")
  endif()
  set_source_files_properties(${TINYEXR_SOURCES} PROPERTIES COMPILE_FLAGS ${CLANG_COMPILE_FLAGS})
endif()

The -Werror flag promotes warnings to errors, and combined with -Weverything, it makes the build very strict.

Specific Warnings/Errors

The reporter mentions warnings in tinyexr.h including:

• -Wunused-macros
• Other warnings that get promoted to errors

Proposed Solutions

The reporter suggests three possible approaches:

1. Remove -Werror for Clang
2. Provide an option to disable -Werror from outside the project
3. Fix the actual warnings causing the errors

They also provided a detailed patch that addresses the specific warnings by:

• Adding pragma directives to suppress unused macro warnings
• Fixing case sensitivity in Windows header include
• Adding explicit casts to resolve type conversion warnings
• Suppressing tautological comparison warnings where appropriate

Environment

• OS: Windows 11
• Compiler: Clang 20.1.6 x86_64-pc-windows-msvc

This is a legitimate build configuration issue that affects the usability of the library when using Clang, especially for projects that want to link against the provided CMake target.

[syoyo]

Please submit PR