Today we come to talk about the header file in the C language.
The C language program code file extension can only be .c or .h, in other words, C language program code can only be written in a file that extension is .c or .h. We call the .h file called header files. The header file can be referenced in the .C file or reference it in .h file.
What is the header file to do? Let's see a program code.
The left is the source code, and the right is the execution result. The function of this code is to print the string "Hello, World!".
We can see that the first line of the source code file is "#include", that is, the header file stdio.h is referenced. Now let's take this line, and then take a look at the results.
Note: The C language plus double slash "//" represents the comment, that is, remove this line of code.
At this time, we found that the result column behind the right, why? This is because the print statement is the printf function output, and the PrintF function is declared in the header file stdio.h, remove the reference stdio.h this line, the code can't find the printf function when compiling, so I'm an error. .
Some friends ask, do we do not quote the header file, can you put the printf function in the .C file? sure. However, Printf is a common function, almost every .c file is used, there are many functions that use the frequency of frequent frequency, even hundreds, there are many. C files in a project, each .C file Hundreds of functions declare, is it hard to see? Moreover, we just want to call these functions directly, do not care about these functions, why bother to list it in our .c file?
The C language provides us with many universal functions, such as copy functions, comparison functions, etc., placed in a universal library for us to use directly, and these functions are placed in some standard header files, stdio. H is one of the standard header files. We can directly call the functions declared in the header file without the need to implement these functions. Of course, in addition to citing standard header files, we can also create and write head files yourself according to actual needs.
Then can the content of the header file can only be a function declaration? of course not. In addition to function declarations, variable definitions, structural definitions, macro definitions can be placed in the header file, if you think that a function you write is high, you can put it in the header file. All in all, generic things can be placed in the header file.
The reference to the header file can be written into "#include" or written "#include" stdio.h ", like the following figure.
The header file is enclosed in a sharp bracket and the meaning of the quotation is different. The former means that the compiler will go directly to the C-function library or the path to the user configured to find it, and will not look for the current directory. The latter means that the compiler will go in the current directory, if the current directory can't find, go to the C-function library or the path to the user configured to find. The current directory mentioned here, you can understand the directory where the files of the reference header file are set.
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