/Zc:inline (Remove unreferenced COMDAT)

Removes unreferenced data or functions that are COMDATs, or that only have internal linkage. Under /Zc:inline, the compiler specifies that translation units with inline data or functions must also include their definitions.

Syntax

/Zc:inline[-]

Remarks

When /Zc:inline is specified, the compiler doesn't emit symbol information for unreferenced COMDAT functions or data. Or, for data or functions that have internal linkage only. This optimization simplifies some of the work the linker does in release builds, or when you specify the /OPT:REF linker option. This compiler optimization can significantly reduce .obj file size and improve linker speeds. The compiler option isn't enabled when you disable optimizations (/Od). Or, when you specify /GL (Whole Program Optimization).

By default, this option is off (/Zc:inline-) in command-line builds. The /permissive- option doesn't enable /Zc:inline. In MSBuild projects, the option is set by the Configuration Properties > C/C++ > Language > Remove unreferenced code and data property, which is set to Yes by default.

If /Zc:inline is specified, the compiler enforces the C++11 requirement that all functions declared inline must have a definition available in the same translation unit if they're used. When the option isn't specified, the Microsoft compiler allows non-conformant code that invokes functions declared inline even if no definition is visible. For more information, see the C++11 standard, in section 3.2 and section 7.1.2. This compiler option was introduced in Visual Studio 2013 Update 2.

To use the /Zc:inline option, update non-conforming code.

This example shows how the non-conforming use of an inline function declaration without a definition still compiles and links when the default /Zc:inline- option is used:

Source file example.h:

// example.h
// Compile by using: cl /W4 /EHsc /O2 zcinline.cpp example.cpp
#pragma once

class Example {
public:
   inline void inline_call(); // declared but not defined inline
   void normal_call();
   Example() {};
};

Source file example.cpp:

// example.cpp
// Compile by using: cl /W4 /EHsc /O2 zcinline.cpp example.cpp
#include <stdio.h>
#include "example.h"

void Example::inline_call() {
   printf("inline_call was called.\n");
}

void Example::normal_call() {
   printf("normal_call was called.\n");
   inline_call(); // with /Zc:inline-, inline_call forced into .obj file
}

Source file zcinline.cpp:

// zcinline.cpp
// Compile by using: cl /W4 /EHsc /O2 zcinline.cpp example.cpp
#include "example.h"

int main() {
   Example example;
   example.inline_call(); // normal call when definition unavailable
}

When /Zc:inline is enabled, the same code causes a LNK2019 error, because the compiler doesn't emit a non-inlined code body for Example::inline_call in example.obj. The missing code causes the non-inlined call in main to reference an undefined external symbol.

To resolve this error, you can remove the inline keyword from the declaration of Example::inline_call, or move the definition of Example::inline_call into the header file, or move the implementation of Example into main.cpp. The next example moves the definition into the header file, where it's visible to any caller that includes the header.

Source file example2.h:

// example2.h
// Compile by using: cl /W4 /EHsc /O2 zcinline2.cpp example2.cpp
#pragma once
#include <stdio.h>

class Example2 {
public:
   inline void inline_call() {
      printf("inline_call was called.\n");
   }
   void normal_call();
   Example2() {};
};

Source file example2.cpp:

// example2.cpp
// Compile by using: cl /W4 /EHsc /O2 zcinline2.cpp example2.cpp
#include "example2.h"

void Example2::normal_call() {
   printf("normal_call was called.\n");
   inline_call();
}

Source file zcinline2.h:

// zcinline2.cpp
// Compile by using: cl /W4 /EHsc /O2 zcinline2.cpp example2.cpp
#include "example2.h"

int main() {
   Example2 example2;
   example2.inline_call(); // normal call when definition unavailable
}

For more information about conformance issues in Visual C++, see Nonstandard behavior.

To set this compiler option in the Visual Studio development environment

1. Open the project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.

2. Select the Configuration Properties > C/C++ > Language property page.

3. Modify the Remove unreferenced code and data property, and then choose OK.

See also

/Zc (Conformance)