warning pragma

Enables selective modification of the behavior of compiler warning messages.

Syntax

#pragma warning(
 warning-specifier : warning-number-list
 [; warning-specifier : warning-number-list ... ] )
#pragma warning( push [ , n ] )
#pragma warning( pop )

Remarks

The following warning-specifier parameters are available.

warning-specifier	Meaning
1, 2, 3, 4	Apply the given level to the specified warnings. Also turns on a specified warning that is off by default.
default	Reset warning behavior to its default value. Also turns on a specified warning that is off by default. The warning will be generated at its default, documented, level. For more information, see Compiler warnings that are off by default.
disable	Don't issue the specified warning messages.
error	Report the specified warnings as errors.
once	Display the specified message(s) only one time.
suppress	Pushes the current state of the pragma on the stack, disables the specified warning for the next line, and then pops the warning stack so that the pragma state is reset.

The following code statement illustrates that a warning-number-list parameter can contain multiple warning numbers, and that multiple warning-specifier parameters can be specified in the same pragma directive.

#pragma warning( disable : 4507 34; once : 4385; error : 164 )

This directive is functionally equivalent to the following code:

// Disable warning messages 4507 and 4034.
#pragma warning( disable : 4507 34 )

// Issue warning C4385 only once.
#pragma warning( once : 4385 )

// Report warning C4164 as an error.
#pragma warning( error : 164 )

The compiler adds 4000 to any warning number that is between 0 and 999.

Warning numbers in the range 4700-4999 are associated with code generation. For these warnings, the state of the warning in effect when the compiler reaches the function definition remains in effect for the rest of the function. Use of the warning pragma in the function to change the state of a warning number larger than 4699 only takes effect after the end of the function. The following example shows the correct placement of a warning pragma to disable a code-generation warning message, and then to restore it.

// pragma_warning.cpp
// compile with: /W1
#pragma warning(disable:4700)
void Test() {
   int x;
   int y = x;   // no C4700 here
   #pragma warning(default:4700)   // C4700 enabled after Test ends
}

int main() {
   int x;
   int y = x;   // C4700
}

Notice that throughout a function body, the last setting of the warning pragma will be in effect for the whole function.

Push and pop

The warning pragma also supports the following syntax, where the optional n parameter represents a warning level (1 through 4).

#pragma warning( push [ , n ] )

#pragma warning( pop )

The pragma warning( push ) stores the current warning state for every warning. The pragma warning( push, n ) stores the current state for every warning and sets the global warning level to n.

The pragma warning( pop ) pops the last warning state pushed onto the stack. Any changes that you made to the warning state between push and pop are undone. Consider this example:

#pragma warning( push )
#pragma warning( disable : 4705 )
#pragma warning( disable : 4706 )
#pragma warning( disable : 4707 )
// Some code
#pragma warning( pop )

At the end of this code, pop restores the state of every warning (includes 4705, 4706, and 4707) to what it was at the start of the code.

When you write header files, you can use push and pop to guarantee that warning-state changes made by a user don't prevent the headers from compiling correctly. Use push at the start of the header and pop at the end. For example, you may have a header that doesn't compile cleanly at warning level 4. The following code changes the warning level to 3, and then restores the original warning level at the end of the header.

#pragma warning( push, 3 )
// Declarations/definitions
#pragma warning( pop )

For more information about compiler options that help you suppress warnings, see /FI and /w.

See also

Pragma directives and the __pragma and _Pragma keywords