AN3350 datasheet(124/185 Pages) STMICROELECTRONICS

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Using pragmas

AN3350

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Doc ID 018512 Rev 2

Using pragmas

The #pragma preprocessor directive specifies option settings to the compiler to control the

compiler and linker’s code generation.

●

Checking pragma settings

●

Saving and restoring pragma settings

●

Determining which settings are saved and restored

●

Invalid pragmas

16.1

Checking pragma settings

The preprocessor function __option() returns the state of pragma settings at compile-

time. The syntax is

__option(setting-name)

where setting-name is the name of a pragma that accepts the on, off, and reset

arguments.

If setting-name is on, __option(setting-name) returns 1. If setting-name is off,

__option(setting-name)

returns 0. If setting-name is not the name of a pragma,

__option(setting-name)

returns false. If setting-name is the name of a pragma that

does not accept the on, off, and reset arguments, the compiler issues a warning

message.

Example 74 shows an example.

Example 74 Using the __option() preprocessor function

#if __option(ANSI_strict)

#include "portable.h" /* Use the portable declarations. */

#else

#include "custom.h" /* Use the specialized declarations. */

#endif

16.2

Saving and restoring pragma settings

There are some occasions when you would like to apply pragma settings to a piece of

source code independently from the settings in the rest of the source file. For example, a

function might require unique optimization settings that should not be used in the rest of the

function’s source file.

Remembering which pragmas to save and restore is tedious and error-prone. Fortunately,

the compiler has mechanisms that save and restore pragma settings at compile time.

Pragma settings may be saved and restored at two levels:

●

All pragma settings

●

Some individual pragma settings

Settings may be saved at one point in a compilation unit (a source code file and the files that

it includes), changed, then restored later in the same compilation unit. Pragma settings

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