gcc背后的库函数和opencv
生成静态库和动态库文件
在桌面上建立目录，导航到目录，在建立三个文件，hello.c main.c hello.h
mkdir a ，cd a， touch hello.c main.c hello.h
分别编辑程序
//hello.c
#include<stdio.h>
void hello(const char *name)
{
printf("Hello %s!\n",name);
}
//main.c
#include <stdio.h>
#include "hello.h"
int main()
{
hello("everyone");
return 0;
}
//hello.h
#ifndef _HELLO_H_
#define _HELLO_H_
#include<stdio.h>
void hello(const char *name)；
#endif
建立hello.o文件
shu@shu-virtual-machine:~$ cd ~/桌面/a
shu@shu-virtual-machine:~/桌面/a$ touch hello.c
shu@shu-virtual-machine:~/桌面/a$ gedit hello.c
shu@shu-virtual-machine:~/桌面/a$ gcc -c hello.c
shu@shu-virtual-machine:~/桌面/a$ ls
hello.c hello.h hello.o main.c
有了hello.o目标文件，之后可以创建静态库。
用ar -crv libmyhello.a hello.o 函数创建静态库，静态库函数前缀为lib，后缀为.a中间文件名，后面为目标文件。
shu@shu-virtual-machine:~/桌面/a$ ar -crv libmyhello.a hello.o
a - hello.o
shu@shu-virtual-machine:~/桌面/a$ ls
hello.c hello.h hello.o libmyhello.a main.c
shu@shu-virtual-machine:~/桌面/a$
//静态库文件libmyhello.a
在程序中使用静态库,先生成main.o目标文件
shu@shu-virtual-machine:~/桌面/a$ gcc -c main.c
shu@shu-virtual-machine:~/桌面/a$ ls
hello.c hello.h hello.o libmyhello.a main.c main.o
shu@shu-virtual-machine:~/桌面/a$
后面建立可执行文件
shu@shu-virtual-machine:~/桌面/a$ gcc -o 1 main.o libmyhello.a
shu@shu-virtual-machine:~/桌面/a$ ls
1 hello.c hello.h hello.o libmyhello.a main.c main.o
//其中1为可执行文件
运行文件
shu@shu-virtual-machine:~/桌面/a$ ./1
Hello everyone!
删除静态库文件在执行文件
shu@shu-virtual-machine:~/桌面/a$ rm -rf libmyhello.a
shu@shu-virtual-machine:~/桌面/a$ ls
1 hello.c hello.h hello.o main.c main.o
shu@shu-virtual-machine:~/桌面/a$ ./1
Hello everyone!
//静态库使用就OK了。
下面进行动态库的使用
首先通过目标文件建立动态库文件前缀为lib，文件名，后缀为.so
gcc命令为gcc -shared -fPIC -o libmyhello.so hello.o
root@shu-virtual-machine:~/桌面/a# gcc -shared -fPIC -o libmyhello.so hello.o
root@shu-virtual-machine:~/桌面/a# ls
1 2 hello.c hello.h hello.o libmyhello.a libmyhello.so main.c main.o
接下来就是使用动态库，将libmyhello.so移动到/usr/lib
sudo cp libmyhello.so /usr/lib
生成可执行文件，并执行
root@shu-virtual-machine:~/桌面/a# gcc main.c libmyhello.so -o 2
root@shu-virtual-machine:~/桌面/a# ls
1 2 hello.c hello.h hello.o libmyhello.a libmyhello.so main.c main.o
root@shu-virtual-machine:~/桌面/a# ./2
Hello everyone!
root@shu-virtual-
总结：在动态库和静态库同名时系统会优先使用动态库除非强调静态库，在选择动态库的时候，我们要将自己定义的动态库放入目录/usr/lib下面
gcc -o 2 main.c -L. lmyhello
静态库和动态库文件的使用
在目录d下面创建相关程序文本文件
shu@shu-virtual-machine:~/桌面$ cd d
shu@shu-virtual-machine:~/桌面/d$ touch 1.c 2.c 3.h 4.c
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 2.c 3.h 4.c
//1.c
#include<stdio.h>
void print1(int arg)
{
printf("1 print arg:%d\n",arg);
}
//2.c
#include<stdio.h>
void print2(char *arg)
{
printf("2 print arg:%s\n",arg);
}
//3.h
#ifndef _3_H_
#define _3_H_
#include<stdio.h>
void print1(int);
void print2(char *);
#endif
//4.c
#include<stdio.h>
#include"3.h"
int main()
{
print1(1);
print2("test");
return 0;
}
生成目标文件后在生成静态库
shu@shu-virtual-machine:~/桌面/d$ gcc -c 1.c 2.c
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c
shu@shu-virtual-machine:~/桌面/d$ ar -crv liball.a 1.o 2.o
a - 1.o
a - 2.o
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c liball.a
执行静态库文件和主程序
shu@shu-virtual-machine:~/桌面/d$ gcc -o all 4.c -L. -lall
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c all liball.a
shu@shu-virtual-machine:~/桌面/d$ ./all
1 print arg:1
2 print arg:test
生成动态库文件
shu@shu-virtual-machine:~/桌面/d$ gcc -c -fPIC 1.c 2.c
//生成fpic目标文件才能使后面编译动态库时不出错误
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c all liball.a
shu@shu-virtual-machine:~/桌面/d$ gcc -shared -fPIC -o liball.so 1.o 2.o
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c all liball.a liball.so
连接动态库并执行主程序
shu@shu-virtual-machine:~/桌面/d$ gcc -o all1 4.c liball.so
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c all all1 liball.a liball.so
//将liball.so移动到/sur/lib目录下，因为系统要先从目录/sur/lib/下面找动态库函数
shu@shu-virtual-machine:~/桌面/d$ sudo cp liball.so /usr/lib
[sudo] shu 的密码：
shu@shu-virtual-machine:~/桌面/d$ ls
1.c 1.o 2.c 2.o 3.h 4.c all all1 liball.a liball.so
shu@shu-virtual-machine:~/桌面/d$ ./all1
1 print arg:1
2 print arg:test
//运行结果如图
编写程序并生成动态库和静态库，运行程序
创建下列函数文本文件
//main.c
#include<stdio.h>
#include"1.h"
int main()
{
int x=4,y=2;
float t=x2x(x,y);
float s=x2y(x,y);
printf("%f\n",t);
printf("%f\n",s);
}
//x2x.c
#include<stdio.h>
float x2x(int x,int y)
{float n=(float)x/y;
return n;
}
//x2y.c
#include<stdio.h>
float x2y(int a,int b)
{
float z=a+b;
return z;
}
//1.h
#ifndef _1_H_
#define _1_H_
#include<stdio.h>
float x2x(int x,int y);
float x2y(int x,int y);
#endif
生成目标文件后生成静态库并执行文件
shu@shu-virtual-machine:~/桌面/c$ gcc -c x2x.c x2y.c
shu@shu-virtual-machine:~/桌面/c$ ls
1.h main.c x2x.c x2x.o x2y.c x2y.o
shu@shu-virtual-machine:~/桌面/c$ ar -crv liball.a x2x.o x2y.o
a - x2x.o
a - x2y.o
shu@shu-virtual-machine:~/桌面/c$ ls
1.h liball.a main.c x2x.c x2x.o x2y.c x2y.o
shu@shu-virtual-machine:~/桌面/c$ gcc -o all main.c -L. -lall
shu@shu-virtual-machine:~/桌面/c$ ls
1.h all liball.a main.c x2x.c x2x.o x2y.c x2y.o
shu@shu-virtual-machine:~/桌面/c$ ./all
2.000000
6.000000
生成动态库并执行
shu@shu-virtual-machine:~/桌面/c$ gcc -c -fPIC x2x.c x2y.c
shu@shu-virtual-machine:~/桌面/c$ gcc -shared -fPIC -o liball.so x2x.o x2y.o
shu@shu-virtual-machine:~/桌面/c$ ls
1.h all liball.a liball.so main.c x2x.c x2x.o x2y.c x2y.o
shu@shu-virtual-machine:~/桌面/c$ sudo cp liball.so /usr/lib
shu@shu-virtual-machine:~/桌面/c$ ls
1.h all liball.a liball.so main.c x2x.c x2x.o x2y.c x2y.o
shu@shu-virtual-machine:~/桌面/c$ gcc main.c liball.so -o all1
shu@shu-virtual-machine:~/桌面/c$ ls
1.h all all1 liball.a liball.so main.c x2x.c x2x.o x2y.c x2y.o
shu@shu-virtual-machine:~/桌面/c$ ./all1
2.000000
6.000000
linux gcc下常用命令
创建文本文件并理解编译过程
shu@shu-virtual-machine:~$ cd ~/桌面/e
shu@shu-virtual-machine:~/桌面/e$ touch main.c
shu@shu-virtual-machine:~/桌面/e$ gedit main.c
shu@shu-virtual-machine:~/桌面/e$ gcc -E main.c -o main.i
shu@shu-virtual-machine:~/桌面/e$ ls
main.c main.i
对main.c进行预处理
接下来对main.c进行汇编
shu@shu-virtual-machine:~/桌面/e$ gcc -s main.i -o main.s
shu@shu-virtual-machine:~/桌面/e$ ls
main.c main.i main.s
之后可以对其进行汇编文件，生成目标文件
shu@shu-virtual-machine:~/桌面/e$ gcc -c main.c
shu@shu-virtual-machine:~/桌面/e$ ls
main.c main.i main.o main.s
shu@shu-virtual-machine:~/桌面/e$
最后对目标文件进行封装连接
shu@shu-virtual-machine:~/桌面/e$ gcc main.o -o main
shu@shu-virtual-machine:~/桌面/e$ ls
main main.c main.i main.o main.s
编译目标文件，其实是在系统目录下找到include库函数
shu@shu-virtual-machine:~/桌面/e$ gcc -c -I /usr/dev/mysql/include main.c -o 1
shu@shu-virtual-machine:~/桌面/e$ ls
1 main main.c main.i main.o main.s
//1为目标文件
在目录下找到相关文件连接到可执行文件
shu@shu-virtual-machine:~/桌面/e$ gcc main.o -o 2
shu@shu-virtual-machine:~/桌面/e$ ./2
hello world
分析gcc编译后的相关文件
shu@shu-virtual-machine:~/桌面/e$ gcc main.c -o main
shu@shu-virtual-machine:~/桌面/e$ size main
text data bss dec hex filename
1182 552 8 1742 6ce main
动态库连接，用size来查看大小
hu@shu-virtual-machine:~/桌面/e$ ldd main
linux-vdso.so.1 => (0x00007ffe1f276000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f30bb206000)
/lib64/ld-linux-x86-64.so.2 (0x00007f30bb5d0000)
//用来查看执行目标引用了哪些动态库文件
静态库连接
shu@shu-virtual-machine:~/桌面/e$ gcc -static main.c -o main1
shu@shu-virtual-machine:~/桌面/e$ size main1
text data bss dec hex filename
824102 7284 6360 837746 cc872 main1
//size可以用来查看大小，观察静态库连接过程
shu@shu-virtual-machine:~/桌面/e$ ldd main1
不是动态可执行文件
//说明没有动态连接
分析生成的文件格式
shu@shu-virtual-machine:~/桌面/e$ readelf -S main
共有 31 个节头，从偏移量 0x19d8 开始：
节头：
[号] 名称 类型 地址 偏移量
大小 全体大小 旗标 链接 信息 对齐
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .interp PROGBITS 0000000000400238 00000238
000000000000001c 0000000000000000 A 0 0 1
[ 2] .note.ABI-tag NOTE 0000000000400254 00000254
0000000000000020 0000000000000000 A 0 0 4
[ 3] .note.gnu.build-i NOTE 0000000000400274 00000274
0000000000000024 0000000000000000 A 0 0 4
[ 4] .gnu.hash GNU_HASH 0000000000400298 00000298
000000000000001c 0000000000000000 A 5 0 8
[ 5] .dynsym DYNSYM 00000000004002b8 000002b8
0000000000000060 0000000000000018 A 6 1 8
[ 6] .dynstr STRTAB 0000000000400318 00000318
000000000000003d 0000000000000000 A 0 0 1
[ 7] .gnu.version VERSYM 0000000000400356 00000356
0000000000000008 0000000000000002 A 5 0 2
[ 8] .gnu.version_r VERNEED 0000000000400360 00000360
0000000000000020 0000000000000000 A 6 1 8
[ 9] .rela.dyn RELA 0000000000400380 00000380
0000000000000018 0000000000000018 A 5 0 8
[10] .rela.plt RELA 0000000000400398 00000398
0000000000000030 0000000000000018 AI 5 24 8
[11] .init PROGBITS 00000000004003c8 000003c8
000000000000001a 0000000000000000 AX 0 0 4
[12] .plt PROGBITS 00000000004003f0 000003f0
0000000000000030 0000000000000010 AX 0 0 16
[13] .plt.got PROGBITS 0000000000400420 00000420
0000000000000008 0000000000000000 AX 0 0 8
[14] .text PROGBITS 0000000000400430 00000430
0000000000000182 0000000000000000 AX 0 0 16
[15] .fini PROGBITS 00000000004005b4 000005b4
0000000000000009 0000000000000000 AX 0 0 4
[16] .rodata PROGBITS 00000000004005c0 000005c0
0000000000000010 0000000000000000 A 0 0 4
[17] .eh_frame_hdr PROGBITS 00000000004005d0 000005d0
0000000000000034 0000000000000000 A 0 0 4
[18] .eh_frame PROGBITS 0000000000400608 00000608
00000000000000f4 0000000000000000 A 0 0 8
[19] .init_array INIT_ARRAY 0000000000600e10 00000e10
0000000000000008 0000000000000000 WA 0 0 8
[20] .fini_array FINI_ARRAY 0000000000600e18 00000e18
0000000000000008 00000000
反汇编ELF，使用相关指令将其反汇编
shu@shu-virtual-machine:~/桌面/e$ objdump -D main
main： 文件格式 elf64-x86-64
Disassembly of section .interp:
0000000000400238 <.interp>:
400238: 2f (bad)
400239: 6c insb (%dx),%es:(%rdi)
40023a: 69 62 36 34 2f 6c 64 imul $0x646c2f34,0x36(%rdx),%esp
400241: 2d 6c 69 6e 75 sub $0x756e696c,%eax
400246: 78 2d js 400275 <_init-0x153>
400248: 78 38 js 400282 <_init-0x146>
40024a: 36 2d 36 34 2e 73 ss sub $0x732e3436,%eax
400250: 6f outsl %ds:(%rsi),(%dx)
400251: 2e 32 00 xor %cs:(%rax),%al
Disassembly of section .note.ABI-tag:
0000000000400254 <.note.ABI-tag>:
400254: 04 00 add $0x0,%al
400256: 00 00 add %al,(%rax)
400258: 10 00 adc %al,(%rax)
40025a: 00 00 add %al,(%rax)
40025c: 01 00 add %eax,(%rax)
40025e: 00 00 add %al,(%rax)
400260: 47 rex.RXB
400261: 4e 55 rex.WRX push %rbp
400263: 00 00 add %al,(%rax)
400265: 00 00 add %al,(%rax)
400267: 00 02 add %al,(%rdx)
400269: 00 00 add %al,(%rax)
40026b: 00 06 add %al,(%rsi)
40026d: 00 00 add %al,(%rax)
40026f: 00 20 add %ah,(%rax)
400271: 00 00 add %al,(%rax)
...
opencv下的 图像处理技术
安装opencv之后进行下列操作
opencv安装博客上有很多教程
创建目录创建文本文件代码如下
在编译代码时要在同一个目录下要保存一张图片为lena.jpg格式
shu@shu-virtual-machine:~/桌面$ mkdir e
shu@shu-virtual-machine:~/桌面$ cd e
shu@shu-virtual-machine:~/桌面/e$ touch code
shu@shu-virtual-machine:~/桌面/e$ gedit code.cpp
shu@shu-virtual-machine:~/桌面/e$ g++ code.cpp -o test1 `pkg-config --cflags --libs opencv`
shu@shu-virtual-machine:~/桌面/e$ ls
code code.cpp test1
shu@shu-virtual-machine:~/桌面/e$ ./test1
shu@shu-virtual-machine:~/桌面/e$ ls
code code.cpp lena.jpg test1 test.png
//code.cpp
#include <opencv2/highgui.hpp>
#include <opencv2/opencv.hpp>
using namespace cv;
using namespace std;
int main(int argc, char** argv)
{
CvPoint center;
double scale = -3;
IplImage* image = cvLoadImage("lena.jpg");
argc == 2? cvLoadImage(argv[1]) : 0;
cvShowImage("Image", image);
if (!image) return -1; center = cvPoint(image->width / 2, image->height / 2);
for (int i = 0;i<image->height;i++)
for (int j = 0;j<image->width;j++) {
double dx = (double)(j - center.x) / center.x;
double dy = (double)(i - center.y) / center.y;
double weight = exp((dx*dx + dy*dy)*scale);
uchar* ptr = &CV_IMAGE_ELEM(image, uchar, i, j * 3);
ptr[0] = cvRound(ptr[0] * weight);
ptr[1] = cvRound(ptr[1] * weight);
ptr[2] = cvRound(ptr[2] * weight);
}
Mat src;Mat dst;
src = cvarrToMat(image);
cv::imwrite("test.png", src);
cvNamedWindow("test",1); imshow("test", src);
cvWaitKey();
return 0;
}
运行结果
原图
运行图
opencv下面，进行视频播放
先进行代码编译和创建
test.cpp
#include <opencv2/opencv.hpp>
using namespace cv;
int main()
{
//从摄像头读取视频
VideoCapture capture("man.mp4");
//循环显示每一帧
while(1){
Mat frame;//定义一个Mat变量，用于存储每一帧的图像
capture >> frame;//读取当前帧
if(frame.empty())//播放完毕，退出
break;
imshow("读取视频帧",frame);//显示当前帧
waitKey(30);//掩饰30ms
}
system("pause");
return 0;
}
在这个目录下要保存一 man.mp4视频
shu@shu-virtual-machine:~/桌面/e$ touch test2.cpp
shu@shu-virtual-machine:~/桌面/e$ gedit test2.cpp
shu@shu-virtual-machine:~/桌面/e$ g++ test2.cpp -o test2 `pkg-config --cflags --libs opencv`
shu@shu-virtual-machine:~/桌面/e$
shu@shu-virtual-machine:~/桌面/e$ ls
code code.cpp lena.jpg man.mp4 test1 test2 test2.cpp test.png
shu@shu-virtual-machine:~/桌面/e$ ./test2
sh: 1: pause: not found
运行结果
opencv下进行录制视频
创建test3.cpp，完成相关编程
/*********************************************************************
打开电脑摄像头，空格控制视频录制，ESC退出并保存视频RecordVideo.avi
*********************************************************************/
#include<iostream>
#include <opencv2/opencv.hpp>
#include<opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
using namespace cv;
using namespace std;
int main()
{
//打开电脑摄像头
VideoCapture cap(0);
if (!cap.isOpened())
{
cout << "error" << endl;
waitKey(0);
return 0;
}
//获得cap的分辨率
int w = static_cast<int>(cap.get(CV_CAP_PROP_FRAME_WIDTH));
int h = static_cast<int>(cap.get(CV_CAP_PROP_FRAME_HEIGHT));
Size videoSize(w, h);
VideoWriter writer("RecordVideo.avi", CV_FOURCC('M', 'J', 'P', 'G'), 25, videoSize);
Mat frame;
int key;//记录键盘按键
char startOrStop = 1;//0 开始录制视频； 1 结束录制视频
char flag = 0;//正在录制标志 0-不在录制； 1-正在录制
while (1)
{
cap >> frame;
key = waitKey(100);
if (key == 32)//按下空格开始录制、暂停录制 可以来回切换
{
startOrStop = 1 - startOrStop;
if (startOrStop == 0)
{
flag = 1;
}
}
if (key == 27)//按下ESC退出整个程序，保存视频文件到磁盘
{
break;
}
if (startOrStop == 0 && flag==1)
{
writer << frame;
cout << "recording" << endl;
}
else if (startOrStop == 1)
{
flag = 0;
cout << "end recording" << endl;
}
imshow("picture", frame);
}
cap.release();
writer.release();
destroyAllWindows();
return 0;
}
shu@shu-virtual-machine:~/桌面/e$ g++ test3.cpp -o test3 `pkg-config --cflags --libs opencv`
shu@shu-virtual-machine:~/桌面/e$ ls
code code.cpp lena.jpg man.mp4 test1 test2 test2.cpp test3 test3.cpp test.png
shu@shu-virtual-machine:~/桌面/e$ ./test3
end recording
end recording
end recording
end recording
end recording
end recording
end recording
end recording
end recording
end recording
end recording
end recording
recording
recording
recording
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recording
shu@shu-virtual-machine:~/桌面/e$ ls
code code.cpp lena.jpg man.mp4 RecordVideo.avi test1 test2 test2.cpp test3 test3.cpp test.png
录制成功后生成.avi文件
