#if 0 to block out code sections

最新推荐文章于 2025-11-29 11:32:53 发布

转载最新推荐文章于 2025-11-29 11:32:53 发布 · 128 阅读

0 ·

CC 4.0 BY-SA版权

原文链接：https://riptutorial.com/c/example/5407/sharpif-0-to-block-out-code-sections

文章标签：

#c语言

c program 专栏收录该内容

6 篇文章

订阅专栏

本文介绍了如何在C语言中利用#if0预处理器指令来屏蔽或临时禁用代码块，以避免注释引起的编译问题。相比于使用块注释，#if0提供了一种更安全的方法，可以更容易地找到并恢复被屏蔽的代码，并且支持嵌套。此外，文章还提到了使用特定宏定义作为条件注释的替代方案，以便在将来查找和管理被屏蔽的代码。

reference:C Language Tutorial => #if 0 to block out code sectionsLearn C Language - #if 0 to block out code sectionshttps://riptutorial.com/c/example/5407/sharpif-0-to-block-out-code-sections

Example#

If there are sections of code that you are considering removing or want to temporarily disable, you can comment it out with a block comment.

/* Block comment around whole function to keep it from getting used.
 * What's even the purpose of this function?
int myUnusedFunction(void)
{
    int i = 5;
    return i;
}
*/

However, if the source code you have surrounded with a block comment has block style comments in the source, the ending */ of the existing block comments can cause your new block comment to be invalid and cause compilation problems.

/* Block comment around whole function to keep it from getting used.
 * What's even the purpose of this function?
int myUnusedFunction(void)
{
    int i = 5;

    /* Return 5 */
    return i;
}
*/

In the previous example, the last two lines of the function and the last '*/' are seen by the compiler, so it would compile with errors. A safer method is to use an #if 0 directive around the code you want to block out.

#if 0
/* #if 0 evaluates to false, so everything between here and the #endif are
 * removed by the preprocessor. */
int myUnusedFunction(void)
{
    int i = 5;
    return i;
}
#endif

A benefit with this is that when you want to go back and find the code, it's much easier to do a search for "#if 0" than searching all your comments.

Another very important benefit is that you can nest commenting out code with #if 0. This cannot be done with comments.

An alternative to using #if 0 is to use a name that will not be #defined but is more descriptive of why the code is being blocked out. For instance if there is a function that seems to be useless dead code you might use #if defined(POSSIBLE_DEAD_CODE) or #if defined(FUTURE_CODE_REL_020201) for code needed once other functionality is in place or something similar. Then when going back through to remove or enable that source, those sections of source are easy to find.