runtime-checks.md

description	title	ms.date	f1_keywords	helpviewer_keywords	no-loc
Learn more about the runtime_checks pragma directive in Microsoft C/C++	runtime_checks pragma	01/22/2021	vc-pragma.runtime_checks runtime_checks_CPP	runtime_checks pragma pragma, runtime_checks	pragma

runtime_checks pragma

Disables or restores the /RTC compiler option settings.

Syntax

#pragma runtime_checks( " [ runtime-check-options ] ", { restore | off } )

Remarks

You can't enable a run-time check that wasn't enabled by a compiler option. For example, if you don't specify /RTCs on the command line, specifying #pragma runtime_checks( "s", restore) won't enable stack frame verification.

The runtime_checks pragma must appear outside a function, and takes effect at the first function defined after the pragma is seen. The restore and off arguments turn options specified in the runtime_checks pragma on or off.

The runtime-check-options can be zero or more of the parameters shown in the following table.

Parameters of the runtime_checks Pragma

Parameter(s)	Type of run-time check
s	Enables stack (frame) verification.
c	Reports when a value is assigned to a smaller data type that results in a data loss.
u	Reports when a variable is used before it's defined.

These parameters are the same ones used with the /RTC compiler option. For example:

#pragma runtime_checks( "sc", restore )

Using the runtime_checks pragma with the empty string ("") is a special form of the directive:

• When you use the off parameter, it turns the run-time error checks listed in the table above, off.

• When you use the restore parameter, it resets the run-time error checks to the ones that you specified using the /RTC compiler option.

#pragma runtime_checks( "", off )
/* runtime checks are off in this region */
#pragma runtime_checks( "", restore )

See also

Pragma directives and the __pragma and _Pragma keywords