黑马《linux基础编程》学习笔记（从36到40）

三十六. vim配置文件

 三十七. gcc工作流程

 

 

//在hello文件夹中，已经写好了名为hello.c的文件
[root@VM_0_15_centos home]# cd hello
[root@VM_0_15_centos hello]# ls
hello.c

//方法一：
//首先预处理
[root@VM_0_15_centos hello]# gcc -E hello.c -o hello.i
[root@VM_0_15_centos hello]# ls
hello.c  hello.i
[root@VM_0_15_centos hello]# vi hello.i
//然后编译c文件成会汇编文件
[root@VM_0_15_centos hello]# gcc -S hello.i -o hello.s
[root@VM_0_15_centos hello]# vi hello.s
//然后把汇编文件，变成二进制文件
[root@VM_0_15_centos hello]# gcc -c hello.s -o hello.o
[root@VM_0_15_centos hello]# vi hello.o
//最后进行链接
[root@VM_0_15_centos hello]# gcc hello.o -o hello
[root@VM_0_15_centos hello]# ls
hello  hello.c  hello.i  hello.o  hello.s

//方法二：
//可以直接如下所示，但不指定名字的话，默认生成名为a.out的可执行文件
[root@VM_0_15_centos hello]# gcc hello.o
[root@VM_0_15_centos hello]# ls
a.out  hello  hello.c  hello.i  hello.o  hello.s

//方法三，可以指定生成的可执行文件的名字
[root@VM_0_15_centos hello]# gcc hello.c -o result
[root@VM_0_15_centos hello]# ls
a.out  hello.c  hello.i  hello.o  hello.s  result
[root@VM_0_15_centos hello]# ./result
hello world[root@VM_0_15_centos hello]#

 

 在这四个流程里，最花费时间的，是编译过程，也就是将预处理后的c文件，变为汇编文件这个过程

 

三十八. gcc的参数 -l

 

 

 首先我们有如图所示文件目录结构

[root@VM_0_15_centos home]# tree experiment/
experiment/
|-- include
|   `-- head.h
`-- sum.c

1 directory, 2 files

 然后这里的sum.c

#include 
#include "head.h"

#define DEBUG

int main()
{
    int a = NUM1;
    int b = NUM2;
    int sum = a+b;

    #ifdef DEBUG
        printf("The sum value is:%d + %d =%d\n",a,b,sum);
    #endif
        return 0;
}

 这里的head.h

#ifndef __HEAD_H__
#define __HEAD_H__

#define NUM1 10
#define NUM2 20

#endif

接下来我们试着用gcc编译

[root@VM_0_15_centos experiment]# ls
include  sum.c
[root@VM_0_15_centos experiment]# gcc sum.c -o sum
sum.c:2:18: fatal error: head.h: No such file or directory
 #include "head.h"
                  ^
compilation terminated.


//上面没有引入参数I来指定头文件所在目录，这里改正后就ok了
[root@VM_0_15_centos experiment]# gcc sum.c -I ./include/ -o sum
[root@VM_0_15_centos experiment]# ls
include  sum  sum.c
[root@VM_0_15_centos experiment]# ./sum
The sum value is:10 + 20 =30

 

 三十九. gcc的参数

-c参数的使用

[root@VM_0_15_centos experiment]# ls
include  sum  sum.c
[root@VM_0_15_centos experiment]# gcc sum.c -c -I ./include/
[root@VM_0_15_centos experiment]# ls
include  sum  sum.c  sum.o
[root@VM_0_15_centos experiment]# file sum.o
sum.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
[root@VM_0_15_centos experiment]# file sum.c
sum.c: C source, ASCII text
[root@VM_0_15_centos experiment]# file sum
sum: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=63370d37cd31aa192241fcfaa8194e9eccd028e2, not stripped

-g参数的使用

显然当加入调试的-g参数后，最终文件大了一些 

 比如多一个d的，有调试模式的，会大很多

 

接下来我们去使用gcc的-D参数

#include 
#include "head.h"

//这里我们注释掉了下面这行，以演示gcc中的-D参数
//#define DEBUG

int main()
{
        int a = NUM1;
        int b = NUM2;
        int sum = a+b;

#ifdef DEBUG
        printf("The sum value is:%d + %d =%d\n",a,b,sum);
#endif
        return 0;
}
[root@VM_0_15_centos experiment]#

然后我们运行一下，就知道-D的意义在于让宏强行生效，所以多用于测试阶段

[root@VM_0_15_centos experiment]# ls
include  sum  sum.c  sum.o  sum_plus
[root@VM_0_15_centos experiment]# gcc sum.c -I ./include/ -o sum1
[root@VM_0_15_centos experiment]# ls
include  sum  sum1  sum.c  sum.o  sum_plus
[root@VM_0_15_centos experiment]# ./sum1
[root@VM_0_15_centos experiment]# gcc sum.c -I ./include/ -o sum2 -D DEBUG
[root@VM_0_15_centos experiment]# ls
include  sum  sum1  sum2  sum.c  sum.o  sum_plus
[root@VM_0_15_centos experiment]# ./sum2
The sum value is:10 + 20 =30

 

接下来我们看一下-Wall参数

首先把sum.c改成有warning的情况

#include 
#include "head.h"

//这里我们注释掉了下面这行，以演示gcc中的-D参数
//#define DEBUG

int main()
{
        int a = NUM1;
        int b = NUM2;
        //This line is writen to show the -Wall parameter in gcc
        int aa;

        int sum = a+b;

#ifdef DEBUG
        printf("The sum value is:%d + %d =%d\n",a,b,sum);
#endif
        return 0;
}

然后在gcc中使用-Wall 参数

[root@VM_0_15_centos experiment]# vi sum.c
[root@VM_0_15_centos experiment]# ls
include  sum  sum1  sum2  sum.c  sum.o  sum_plus
[root@VM_0_15_centos experiment]# gcc sum.c -I ./include/ -D DEBUG -o sum_wall -Wall
sum.c: In function ‘main’:
sum.c:12:6: warning: unused variable ‘aa’ [-Wunused-variable]
  int aa;
      ^
[root@VM_0_15_centos experiment]#

 

四十. 库的使用