[C] C Programming Q & A - 01

yanglsw

Just want to share some common C programming questions and answers here, if anyone has a better answer or comments, please feel free to reply, in either Chinese or English.  Hope everyone can learn from each other and share knowledge.


What is the difference between #include <file> and #include “file”?

Answers:

When writing your C program, you can include files in two ways. The first way is to surround the file you want to include with the angled brackets < and >. This method of inclusion tells the preprocessor to look for the file in the predefined default location. This predefined default location is often an INCLUDE environment variable that denotes the path to your include files. For instance, given the INCLUDE variable

INCLUDE=C:COMPILERINCLUDE;S:SOURCEHEADERS;

using the #include <file> version of file inclusion, the compiler first checks the C:COMPILERINCLUDE
directory for the specified file. If the file is not found there, the compiler then checks the
S:SOURCEHEADERS directory. If the file is still not found, the preprocessor checks the current directory.

The second way to include files is to surround the file you want to include with double quotation marks " ". This method of inclusion tells the preprocessor to look for the file in the current directory first, then look for it in the predefined locations you have set up. Using the #include “file” version of file inclusion and applying it to the preceding example, the preprocessor first checks the current directory for the specified file. If the file is not found in the current directory, the C:COMPILERINCLUDE directory is searched. If the file is still not found, the preprocessor checks the S:SOURCEHEADERS directory.

The #include <file> method of file inclusion is often used to include standard headers such as stdio.h or
stdlib.h. This is because these headers are rarely (if ever) modified, and they should always be read from your compiler’s standard include file directory.

The #include “file” method of file inclusion is often used to include nonstandard header files that you have created for use in your program. This is because these headers are often modified in the current directory, and you will want the preprocessor to use your newly modified version of the header rather than the older, unmodified version.

liuwei20s

支持，虽然不能完全看懂，大概了解

pentix81765

我是编程盲啊，谁教教我 QQ727781765

zdhtmp

基础的东西总是错的最多的

rtm

完全是赚分贴，自己发题目自己已经给答案了