string mav转换

c语言版本的

理论

ios::binary

在创建文件流时，可以显示指定它的打开方式为ios::binary，也就是以二进制方式打开。但是，无论是否指定二进制方式打开文件，读写的最小单位都是字节。那么，它到底起到什么作用呢？

首先，介绍一下二进制方式打开与普通打开方式的区别，两者大的区别在于对换行符的处理方式不同。由于历史原因，Windows操作系统是用两个字符(\r\n)来表示换行符的；而Unix操作系统却是用单个字符(\n)来表示换行符的。因此，在创建文件流时，如果指定了以ios::binary方式打开，那么换行符就是单字符的；否则，就采用Windows操作系统的双字符。

总结来说，以ios::binary方式打开，换行符被解释成\n；反之，换行符被解释成\r\n。

所以为了兼容性，通常在Windous系统中通常使用ios::binary方式打开图像文件；在Unix(或类Unix)操作系统中，指定和不指定ios::binary方式没有区别。

图片与char* / char[]的转换

#include  // ifstream, ifstream::in
#include 
#define MAX 1024*1024
using namespace std;

// 将内存中的二进制文件写成一张图片
bool write_image(const string& filename, char  *pBuffer, int length){
    ofstream fout(filename, ios::binary);
    if(!fout){
        printf("can't open  = %s\n", filename.c_str());
        return false;
    }
    fout.write(pBuffer,length);
    fout.close();
    return true;
}
bool write_image2(const string& filename, char  *image_buf, int image_len){
    int fd = open(filename.c_str(), O_CREAT | O_WRONLY | O_TRUNC);
    if (fd > 0) {
        int n = 0, m = 0;
        do {
            m = write(fd, image_buf + n, image_len - n);
            n += m;
        } while (n < image_len);
        close(fd);
    }
}

// 将磁盘中的二进制文件读到内存中
bool read_image(const string& filename, char * pBuffer, int *out_length){
    ifstream fin(filename, ifstream::in | ios::binary);
    if(!fin){
        printf("can't open  = %s\n", filename.c_str());
        return false;
    }

    // 求图片长度
    fin.seekg(0, std::ifstream::end);  //将文件流指针定位到流的末尾
    int length = fin.tellg();
    fin.seekg(0, std::ifstream::beg);  //将文件流指针重新定位到流的开始
    if(length <= 0 || length > MAX){
        printf("length = %d\n", length);
        return false;
    }

    // 读取
    *out_length = length;
    fin.read(pBuffer, length);
    fin.close();
    return true;
}

int main(){
    // 读图片
    char * pBuffer = new char[MAX];
    int length = 0;
    bool succ = read_image( R"(D:\workspace\binarytree\test.jpg)", pBuffer, &length);
    if(succ){
        write_image(R"(D:\workspace\binarytree\save.jpg)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.png)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.txt)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.bmp)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.raw)", pBuffer, length);
    }

    delete [] pBuffer;

    return 0;
}

int main11(){
    // 读图片
    char pBuffer[MAX] = {0};
    int length = 0;
    bool succ = read_image( R"(D:\workspace\binarytree\test.jpg)", pBuffer, &length);
    if(succ){
        write_image(R"(D:\workspace\binarytree\save.jpg)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.png)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.txt)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.bmp)", pBuffer, length);
        write_image(R"(D:\workspace\binarytree\save.raw)", pBuffer, length);
    }


    return 0;
}

等待研究
https://www.cnblogs.com/lyj-blogs/p/10178384.html

结合opencv

cv:mat读取图片并显示

int main()
{
    cv::Mat mat = cv::imread("/home/oceanstar/image/aa.jpg");
    if(mat.empty())
    {
        cout << "图像不能加载！"<< endl;
        return -1;
    }

    imshow("MyWindow", mat);
    //等待直到有键按下
    waitKey(0);
    return 0;
}

char与mat

#include 
#include 
#include 
#include 
#include 

using namespace std;
using namespace cv;

const int MAX = 1024 * 1920 * 3;


bool write_image(const string& filename, char  *pBuffer, int length){
    ofstream fout(filename, ios::binary);
    if(!fout){
        printf("can't open  = %s\n", filename.c_str());
        return false;
    }
    fout.write(pBuffer,length);
    fout.close();
    return true;
}
int main()
{
    //3通道图像
    cv::Mat img2 = cv::imread("/home/oceanstar/image/aa.jpg");
    if(img2.empty())
    {
        cout << "图像不能加载！"<< endl;
        return -1;
    }

    char p[MAX]; //char数组
    std::vector<uchar> buff;
    cv::imencode(".jpg", img2, buff);
    memset(p, 0, MAX);
    memcpy(p, reinterpret_cast<char*>(&buff[0]), buff.size());
    int length = buff.size();

    char * buffer = reinterpret_cast<char *>(p);
    write_image("/home/oceanstar/image/vvvv.jpg", buffer, length );

    return 0;
}

uchar与mat

#include 
#include 
#include 
#include 
#include 

using namespace std;
using namespace cv;

const int img_width=1920; /** 图像的宽度*/
const int img_height = 1024; /**图像的高度*/


/**将uchar类型的转换为Mat类型*/
Mat ucharToMat(const uchar *p2)
{
    Mat img(Size(img_width, img_height),CV_8UC3);
    for (int i = 0; i < img_width * img_height * 3; i++)
    {
        img.at<Vec3b>(i / (img_width * 3), (i % (img_width * 3)) / 3)[i % 3] = p2[i];
    }
    return img;
}
/**数组，存放图片大小*/
///uchar p1[img_width * img_height * 3];
/**将Mat类型的数据转换为uchar类型*/
uchar* matToUchar(Mat img, uchar *p1)
{
    for (int i = 0; i < img_width * img_height * 3; i++)
    {
        p1[i]= (uchar)img.at<Vec3b>(i / (img_width * 3), (i % (img_width * 3)) / 3)[i % 3];
    }
    return p1;
}

int main()
{
    //3通道图像
    cv::Mat img2 = cv::imread("/home/oceanstar/image/aa.jpg");
    if(img2.empty())
    {
        cout << "图像不能加载！"<< endl;
        return -1;
    }

    /**定义一个数组存放matToUchar的返回值*/
    auto *p = new uchar[img_width * img_height * 3];
    matToUchar(img2, p);
    /**下面这两行代码目的是输出Mat转化为uchar的值是否正确
    @(int)目的是将uchar类型的数据转换为int可以直观的看到，
    uchar的数据输出的是乱码
    */
   for (int i = 0; i < img_width * img_height * 3; i++){
        cout << (int)p[i] << endl;
    }
    Mat img = ucharToMat(p);
    imshow("img",img);
    waitKey(0);

    return 0;
}

https://blog.csdn.net/Black_Friend/article/details/89372976

cv::Mat转std::string

cv::Mat mat = cv::imread("d:\\1.jpg");
std::string str;
std::vector<unsigned char> buff;
cv::imencode(".jpg", mat, buff);
str.resize(buff.size());
memcpy(&str[0], buff.data(), buff.size());

https://www.cnblogs.com/mdumpling/p/8179167.html