Clang error: unable to open output file 'A': 'B' (err_fe_unable_to_open_output)

Text	error: unable to open output file 'A': 'B'
Type	Error
Category	None
Internal Id	err_fe_unable_to_open_output
Internal Message	unable to open output file '%0': '%1'
Regular Expression	(?:error|fatal error)\: unable to open output file '(.*?)'\: '(.*?)'
First Commit	2009-12-03 7554699afabf Fix CompilerInstance::createOutputFile to use proper diagnostics, and (try to) update all clients to...

Description

The error is issued by the Clang compiler when it encounters a situation that prevents it from opening the specified output file. This could occur for various reasons, such as the directory not existing, insufficient permissions to write to the specified location, or an incorrect or inaccessible file path. The error message consists of two parts: the path the compiler attempted to write to and a message detailing the specific reason it was unable to open that file. Understanding both the context and the reason provided in the error message is crucial for identifying and resolving the issue.

AI Generated

Example

In the following example, the Clang compiler attempts to compile a simple C++ program that includes only a main function, which does nothing. The compilation command is executed with options directing the compiler to output the object file to a non-existent directory. Since the specified output directory does not exist, the compiler is unable to create the output file and subsequently emits an error message. This message details both the path where the compiler attempted to write the output file and the specific reason for the failure, highlighting that the file or directory could not be found. This scenario demonstrates how incorrect or inaccessible file paths can impede the Clang compiler's operations, leading to the generation of an error message as described in the article.

AI Generated

Flags	-xc++ -o /nonexistent/nonexistent.o	[Try out in Compiler Explorer]
Source	int main() {} // Will fail due to non-existent output directory
Compiler Output	error: unable to open output file '/nonexistent/nonexistent.o': 'No such file or directory'

Clang Internals (17.0.6)

Git Commit Message

Fix CompilerInstance::createOutputFile to use proper diagnostics, and (try to) update all clients to be able to handle failure.

llvm-svn: 90437

Used in Clang Sources

This section lists all occurrences of the diagnostic within the Clang's codebase. For each occurrence, an auto-extracted snipped from the source code is listed including key elements like control structures, functions, or classes. It should illustrate the conditions under which the diagnostic is activated.

clang/lib/CodeGen/BackendUtil.cpp (line 150)

class EmitAssemblyHelper {
  // ...
  std::unique_ptr<llvm::ToolOutputFile> openOutputFile(StringRef Path) {
    // ...
    if (EC) {
      Diags.Report(diag::err_fe_unable_to_open_output) << Path << EC.message();

clang/lib/Frontend/CompilerInstance.cpp (line 838)

std::unique_ptr<raw_pwrite_stream> CompilerInstance::createOutputFile(StringRef OutputPath, bool Binary, bool RemoveFileOnSignal, bool UseTemporary, bool CreateMissingDirectories) {
  // ...
  getDiagnostics().Report(diag::err_fe_unable_to_open_output) << OutputPath << errorToErrorCode(OS.takeError()).message();

clang/lib/Frontend/CompilerInstance.cpp (line 2164)

void CompilerInstance::createModuleFromSource(SourceLocation ImportLoc, StringRef ModuleName, StringRef Source) {
  // ...
  if (std::error_code EC = llvm::sys::fs::createTemporaryFile(CleanModuleName, "pcm", ModuleFileName)) {
    getDiagnostics().Report(ImportLoc, diag::err_fe_unable_to_open_output) << ModuleFileName << EC.message();

clang/lib/Frontend/Rewrite/FixItRewriter.cpp (line 108)

bool FixItRewriter::WriteFixedFiles(std::vector<std::pair<std::string, std::string>> *RewrittenFiles) {
  // ...
  for (iterator I = buffer_begin(), E = buffer_end(); I != E; ++I) {
    // ...
    if (EC) {
      Diags.Report(clang::diag::err_fe_unable_to_open_output) << Filename << EC.message();

clang/tools/driver/cc1as_main.cpp (line 376)

static std::unique_ptr<raw_fd_ostream> getOutputStream(StringRef Path, DiagnosticsEngine &Diags, bool Binary) {
  // ...
  if (EC) {
    Diags.Report(diag::err_fe_unable_to_open_output) << Path << EC.message();

Triggered in Clang Tests

This section lists all internal Clang test cases that trigger the diagnostic.

clang/test/Driver/ftime-trace.cpp

• error: unable to open output file '/dev/null.json': 'Permission denied'