C-1 入门知识

分手后的思念是犯贱 2023-02-22 05:19 26阅读 0赞

笔者在`WIN10`和`VC6.0`下学习的笔记。

### 标题 ###

*   *   *  编译
         *   *  预处理
             *  编译和汇编
             *  链接

### 编译 ###

在`VC`安装目录`C:\Program Files (x86)\Microsoft Visual Studio\VC98\Bin`中就是`IDE`编译套件。  
目录文件信息如下：

cl.exe
    link.exe
    c1.dll
    c2.dll
    c1xx.dll

其中`cl`为编译器`（command line）`，其实现位于`c1.dll c2.dll c1.dll`.而`link.exe` 便是链接工具.

首先一个最简单的`hello.cpp`如下：

#include <stdio.h>
    void main(){
        
    	printf("bb");
    	printf("aa");
    }

编译的步骤大致分为四步骤：  
1.预编译  
2.编译  
3.汇编  
4.链接

关于这几步网上到处是轮子，详情请参阅：[c编译流程][c]

我们在`vc`提供的编译套件中手动实现这几步。

#### 预处理 ####

`cl /p hello.cpp` 预编译会将`include`展开放入生成的`hello.i`文件中.(关于更多编译选项 可输入 `cl -help`查看或[c编译选项][c 1])

#line 1 "Cpp1.cpp"
    #line 1 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    
     int __cdecl _fileno(FILE *);
    #line 307 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
     int __cdecl _flushall(void);
     FILE * __cdecl fopen(const char *, const char *);
     int __cdecl fprintf(FILE *, const char *, ...);
     int __cdecl fputc(int, FILE *);
     int __cdecl _fputchar(int);
     int __cdecl fputs(const char *, FILE *);
     size_t __cdecl fread(void *, size_t, size_t, FILE *);
     FILE * __cdecl freopen(const char *, const char *, FILE *);
     int __cdecl fscanf(FILE *, const char *, ...);
     int __cdecl fsetpos(FILE *, const fpos_t *);
     int __cdecl fseek(FILE *, long, int);
     long __cdecl ftell(FILE *);
     size_t __cdecl fwrite(const void *, size_t, size_t, FILE *);
     int __cdecl getc(FILE *);
     int __cdecl getchar(void);
     int __cdecl _getmaxstdio(void);
     char * __cdecl gets(char *);
     int __cdecl _getw(FILE *);
     void __cdecl perror(const char *);
     int __cdecl _pclose(FILE *);
     FILE * __cdecl _popen(const char *, const char *);
     int __cdecl printf(const char *, ...);
     int __cdecl putc(int, FILE *);
     int __cdecl putchar(int);
     int __cdecl puts(const char *);
     int __cdecl _putw(int, FILE *);
     int __cdecl remove(const char *);
     int __cdecl rename(const char *, const char *);
     void __cdecl rewind(FILE *);
     int __cdecl _rmtmp(void);
     int __cdecl scanf(const char *, ...);
     void __cdecl setbuf(FILE *, char *);
     int __cdecl _setmaxstdio(int);
     int __cdecl setvbuf(FILE *, char *, int, size_t);
     int __cdecl _snprintf(char *, size_t, const char *, ...);
     int __cdecl sprintf(char *, const char *, ...);
     int __cdecl sscanf(const char *, const char *, ...);
     char * __cdecl _tempnam(const char *, const char *);
     FILE * __cdecl tmpfile(void);
     char * __cdecl tmpnam(char *);
     int __cdecl ungetc(int, FILE *);
     int __cdecl _unlink(const char *);
     int __cdecl vfprintf(FILE *, const char *, va_list);
     int __cdecl vprintf(const char *, va_list);
     int __cdecl _vsnprintf(char *, size_t, const char *, va_list);
     int __cdecl vsprintf(char *, const char *, va_list);
    
    
    #line 363 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    
    
    
     FILE * __cdecl _wfsopen(const wchar_t *, const wchar_t *, int);
    #line 369 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
     wint_t __cdecl fgetwc(FILE *);
     wint_t __cdecl _fgetwchar(void);
     wint_t __cdecl fputwc(wint_t, FILE *);
     wint_t __cdecl _fputwchar(wint_t);
     wint_t __cdecl getwc(FILE *);
     wint_t __cdecl getwchar(void);
     wint_t __cdecl putwc(wint_t, FILE *);
     wint_t __cdecl putwchar(wint_t);
     wint_t __cdecl ungetwc(wint_t, FILE *);
    
     wchar_t * __cdecl fgetws(wchar_t *, int, FILE *);
     int __cdecl fputws(const wchar_t *, FILE *);
     wchar_t * __cdecl _getws(wchar_t *);
     int __cdecl _putws(const wchar_t *);
    
     int __cdecl fwprintf(FILE *, const wchar_t *, ...);
     int __cdecl wprintf(const wchar_t *, ...);
     int __cdecl _snwprintf(wchar_t *, size_t, const wchar_t *, ...);
     int __cdecl swprintf(wchar_t *, const wchar_t *, ...);
     int __cdecl vfwprintf(FILE *, const wchar_t *, va_list);
     int __cdecl vwprintf(const wchar_t *, va_list);
     int __cdecl _vsnwprintf(wchar_t *, size_t, const wchar_t *, va_list);
     int __cdecl vswprintf(wchar_t *, const wchar_t *, va_list);
     int __cdecl fwscanf(FILE *, const wchar_t *, ...);
     int __cdecl swscanf(const wchar_t *, const wchar_t *, ...);
     int __cdecl wscanf(const wchar_t *, ...);
    
    
     FILE * __cdecl _wfdopen(int, const wchar_t *);
     FILE * __cdecl _wfopen(const wchar_t *, const wchar_t *);
     FILE * __cdecl _wfreopen(const wchar_t *, const wchar_t *, FILE *);
     void __cdecl _wperror(const wchar_t *);
     FILE * __cdecl _wpopen(const wchar_t *, const wchar_t *);
     int __cdecl _wremove(const wchar_t *);
     wchar_t * __cdecl _wtempnam(const wchar_t *, const wchar_t *);
     wchar_t * __cdecl _wtmpnam(wchar_t *);
    
    
    
    #line 414 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    #line 415 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    
    #line 418 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    
    
    
    
    //省略一大批
    
    
    
     int __cdecl fcloseall(void);
     FILE * __cdecl fdopen(int, const char *);
     int __cdecl fgetchar(void);
     int __cdecl fileno(FILE *);
     int __cdecl flushall(void);
     int __cdecl fputchar(int);
     int __cdecl getw(FILE *);
     int __cdecl putw(int, FILE *);
     int __cdecl rmtmp(void);
     char * __cdecl tempnam(const char *, const char *);
     int __cdecl unlink(const char *);
    
    #line 463 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    
    }
    #line 467 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    
    #pragma pack(pop)
    #line 471 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    
    #line 473 "C:\\Program Files (x86)\\Microsoft Visual Studio\\VC98\\include\\stdio.h"
    #line 2 "hello.cpp"
    void main(){
    	printf("bb");
    	printf("aa");
    
    }

第一个问题，我们的`include<stdio.h>`会首先去环境变量的`include`寻找的对应的头文件，如果没有找到那么将去编译目录 也就是`hello.cpp`本文件所在目录寻找`stdio.h`。

笔者所在电脑的`include`环境变量:

C:\Program Files (x86)\Microsoft Visual Studio\VC98\atl\include;
    C:\Program Files (x86)\Microsoft Visual Studio\VC98\mfc\include;
    C:\Program Files (x86)\Microsoft Visual Studio\VC98\include

如果开发者用双引号寻找头文件（`include ""`）那么首先会去编译目录 `helllo.cpp`寻找，如果找不到才会寻找环境变量`include`。

另外可以在预编译的文件中可以看到导入的头文件具体位置。

#### 编译和汇编 ####

笔者并没有在`vc`编译选项中找到，所以我就干脆把这两步骤合为一步。

`cl \c hello.i` 其中`\c`选项为编译但是不连接，`hello.i` 是预处理后的文件.  
运行后目录将生成一个 二进制`hello.obj`文件，此文件可以用`winhex`查看。

#### 链接 ####

`c语言`要运行必须链接实现的实现库，比如我们的`include<stdio.h>`的`printl`函数，只是在预处理的时候导入的声明然而具体的实现其没有，所以我们必须借助`link.exe`链接并生成可执行文件。

我们查看`msdn`文档的`printf`函数，了解到`printf` 实现库存在三个库中，分别为LIBC，LIBCMT，MSVCRT，分别对应`单线程`, `多线程`,`Microsoft visual C RUN TIME`版本实现，我们这里只需要单线程版本。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FmYW5taW5neWlx_size_16_color_FFFFFF_t_70]

所以 我们键入如下命令`link hello.obj LIBC.LIB`完成最终的程序并生成`Hello.exe`

[c]: https://www.cnblogs.com/CarpenterLee/p/5994681.html
[c 1]: http://www.cppblog.com/fenglinuestc/articles/48311.html
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FmYW5taW5neWlx_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/2020070200130321.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FmYW5taW5neWlx,size_16,color_FFFFFF,t_70