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/Zc:strictStrings (Disable string literal type conversion)


The latest version of this topic can be found at -Zc:strictStrings (Disable string literal type conversion).

When specified, the compiler requires strict const-qualification conformance for pointers initialized by using string literals.


If /Zc:strictStrings is specified, the compiler enforces the standard C++ const qualifications for string literals, as type 'array of const``char' or 'array of const``wchar_t', depending on the declaration. String literals are immutable, and an attempt to modify the contents of one results in an access violation error at run time. You must declare a string pointer as const to initialize it by using a string literal, or use an explicit const_cast to initialize a non-const pointer. By default, or if /Zc:strictStrings- is specified, the compiler does not enforce the standard C++ const qualifications for string pointers initialized by using string literals.

Use the /Zc:strictStrings option to prevent compilation of incorrect code. This example shows how a simple declaration error leads to a crash at run time:

// strictStrings_off.cpp  
// compile by using: cl /W4 strictStrings_off.cpp  
int main() {  
   wchar_t* str = L"hello";  
   str[2] = L'a'; // run-time error: access violation  

When /Zc:strictStrings is enabled, the same code reports an error in the declaration of str.

// strictStrings_on.cpp  
// compile by using: cl /Zc:strictStrings /W4 strictStrings_on.cpp  
int main() {  
   wchar_t* str = L"hello"; // error: Conversion from string literal   
   // loses const qualifier  
   str[2] = L'a';   

If you use auto to declare a string pointer, the compiler creates the correct const pointer type declaration for you. An attempt to modify the contents of a const pointer is reported by the compiler as an error.

System_CAPS_ICON_note.jpg Note

The Standard C++ Library in Visual C++ in Visual Studio 2013 does not support the /Zc:strictStrings compiler option in debug builds. If you see several C2665 errors in your build output, this may be the cause.

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 Working with Project Properties.

  2. Select the C/C++ folder.

  3. Select the Command Line property page.

  4. Modify the Additional Options property to include /Zc:strictStrings and then choose OK.

/Zc (Conformance)