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C compiler

AN3350

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Doc ID 018512 Rev 2

C compiler

This chapter explains the implementation of the C programming language:

●

Extensions to standard C

●

C99 extensions

●

GCC extensions

12.1

Extensions to standard C

The C compiler adds extra features to the C programming language. These extensions

make it easier to port source code from other compilers and offer some programming

conveniences. Note that some of these extensions do not conform to the ISO/IEC 9899-

1990 C standard (“C90”).

●

Controlling standard C conformance

●

C++-style comments

●

Unnamed arguments

●

Extensions to the preprocessor

●

Non-standard keywords

12.1.1

Controlling standard C conformance

The compiler offers settings that verify how closely your source code conforms to the

ISO/IEC 9899-1990 C standard (“C90”). Enable these settings to check for possible errors

or improve source code portability.

Some source code is too difficult or time-consuming to change so that it conforms to the

ISO/IEC standard. In this case, disable some or all of these settings.

Table 12 shows how to control the compiler’s features for ISO conformance.

12.1.2

C++-style comments

When ANSI strictness is off, the C compiler allows C++-style comments. Example 23 shows

an example.

Example 23 C++ comments

a = b;

// This is a C++-style comment.

c = d;

/* This is a regular C-style comment. */

Table 12.

Controlling conformance to the ISO/IEC 9899-1990 C language

To control this option from here...

use this setting

Source code

#pragma ANSI_strict

#pragma only_std_keywords

Command line

-ansi

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