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warning

Allows selective modification of the behavior of compiler warning messages.

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

The warning-specifier can be one of the following.

Warning-specifier

Meaning

1, 2, 3, 4

Apply the given level to the specified warning(s). This also has the effect of turning a specified warning on that is off by default.

default

Reset warning behavior to its default value. This also has the effect of turning a specified warning on that is off by default. The warning will be generated at its default, documented, level.

See Compiler Warnings That Are Off by Default for more information.

disable

Do not issue the specified warning message(s).

error

Report the specified warnings as errors.

once

Display the specified message(s) only once.

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, resetting the pragma state. You can only specify one warning for each suppress specifier, but multiple warning pragmas can operate on one line of code.

The warning-number-list can contain any warning numbers. Multiple options can be specified in the same pragma directive as follows:

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

This is functionally equivalent to:

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

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

// Report warning 4164 as an error.
#pragma warning( error : 164 )

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

The compiler only supports up to 56 #pragma warning statements in a compiland.

For warning numbers in the range of 4700-4999, those associated with code generation, the state of the warning in effect when the compiler encounters the open curly brace of a function will be in effect for the rest of the function. Using the warning pragma inside the function to change the state of a warning greater than 4699 will only take effect after the end of the function. The following example shows the correct placement of warning pragmas to disable, and then restore, a code-generation warning message:

// 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
}

Note that within a function body, the last setting of the warning pragma will be in effect for the entire function.

The warning pragma also supports the following syntax:

#pragma warning( push [ ,n ] )

#pragma warning( pop )

Where n represents a warning level (1 through 4).

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

The pragma warning( pop ) pops the last warning state pushed onto the stack. Any changes 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 all warnings (including 4705, 4706, and 4707) to what it was at the beginning of the code.

When you write header files, you can use push and pop to ensure that changes to warning states made by the user do not prevent your headers from compiling properly. Use push at the beginning of the header and pop at the end. Suppose, for example, you have a header that does not compile cleanly at warning level 4. The following code changes the warning level to 3 then restores the original warning level at the end of the header:

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

See /FI and /w for compiler options that help you suppress warnings.

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