C++ 获取图片文件信息

解析图片文件格式，获取图片名称、类型、像素宽高

图片文件格式参考：https://blog.csdn.net/adzcsx2/article/details/50503506

1、ImageFile.cpp:

#include "config.h"
#include "ImageFile.h"
#include <fstream>
#include <stdio.h>
#include <iostream>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <cstring>

namespace blink {

#define JPEG_FILE_TYPE          1
#define BMP_FILE_TYPE           2
#define PNG_FILE_TYPE           3
#define GIF_FILE_TYPE           4

/* 
　　通过文件头标识判断图片格式，
　　jpg： FF, D8
　　bmp： 42 4D
　　gif： 47 49 46 38
　　png： 89 50 4E 47
*/

int check_fileType(const unsigned char *buf)
{
    if(buf[0] == 0xFF && buf[1] == 0xd8 && buf[2] == 0xFF) 
    {
        return JPEG_FILE_TYPE; 
    }
    if(buf[0] == 0x42 && buf[1] == 0x4d)
    {
        return BMP_FILE_TYPE;
    }
    if(buf[0] == 0x47 && buf[1] == 0x49 && buf[2] == 0x46 && buf[3] == 0x38)
    {
        return GIF_FILE_TYPE;
    }
    if(buf[0] == 0x89 && buf[1] == 0x50 && buf[2] == 0x4e && buf[3] == 0x47)
    {
        return PNG_FILE_TYPE;
    }
    else
        return 0;
}


/*在构造函数内获取像素宽高：mwidth、mheigh*/

ImageFile::ImageFile(const String& path)
{
    int type;
    mpath = path;
    mwidth = 0;
    mheight = 0;
    mtype = "";
    src = (char *)path.utf8().data();
    int i = 0;
    int size;
    unsigned char *buff = NULL;
    FILE *fp;
    if((fp = fopen(src,"rb+")) == NULL)
    {
        mtype = "The file was not opened!";
        return;
    }
    fseek(fp,0,SEEK_END);
    size = ftell(fp);
    buff = (unsigned char*)malloc(size);
    if(buff)
        memset(buff,0,size);
    fseek(fp,0,SEEK_SET);   
    if(fread(buff,1,size,fp)!=size)
    {
        mtype ="read error!";
        return;
    } 
    
    type = check_fileType(buff);
    switch(type)
    {
        case JPEG_FILE_TYPE:
            mtype = "jpg file!";
            for(i = 0; i < size ; i++)
            {
                if(buff[i] == 0xff && buff[i+1] == 0xc0)
                {
                    mwidth = (buff[i+7]<<8) | buff[i+8];
                    mheight = (buff[i+5]<<8) | buff[i+6];
                    break;
                }
            }
            break;
            
        case BMP_FILE_TYPE:
            mtype = "bmp file!";
            for(i = 0; i < size ; i++)
            {
                if(buff[i] == 0x28 && buff[i+1] == 0x00)
                {
                    mwidth = (buff[i+7]<<24) | buff[i+6]<<16 | buff[i+5]<<8 | buff[i+4];
                    mheight = (buff[i+11]<<24) | buff[i+10]<<16 | buff[i+9]<<8 | buff[i+8];
                    break;
                }
            }
            break;
            
        case PNG_FILE_TYPE:
            mtype = "png file!";
            for(i = 0; i < size ; i++)
            {
                if(buff[i] == 0x49 && buff[i+1] == 0x48)
                {
                    mheight = (buff[i+8]<<24) | buff[i+9]<<16 | buff[i+10]<<8 | buff[i+11];
                    mwidth = (buff[i+4]<<24) | buff[i+5]<<16 | buff[i+6]<<8 | buff[i+7];
                    break;
                }
            }
            break;
            
        case GIF_FILE_TYPE:
            mtype = "gif file!";
            for(i = 0; i < size ; i++)
            {
                if(buff[i] == 0x00 && buff[i+1] == 0x2c)
                {
                    mwidth = (buff[i+7]<<8) | buff[i+6];
                    mheight = (buff[i+9]<<8) | buff[i+8];
                    break;
                }
            }
            break;
        default:
            break;
    }
    fclose(fp);
    free(buff);
   
}


String ImageFile::type() const
{
    return mtype;
}

String ImageFile::location() const
{
    int length = mpath.length();
    int pos = mpath.reverseFind('/');
    
    while (pos == length - 1)
    {
        pos = mpath.reverseFind('/' ,pos - 1);
        length--;
    }
    
    if (pos < 0)
    {
        return "";
    }
    
    return mpath.substring(0,pos + 1);
}

String ImageFile::fileName() const
{
    int length = mpath.length();
    int pos = mpath.reverseFind('/');
    
    while (pos == length - 1)
    {
        pos = mpath.reverseFind('/' , pos - 1);
        length--;
    }
    
    if (pos < 0)
    {
        return "";
    }
    
    return mpath.substring(pos + 1,length);
}

double ImageFile::width() const
{
    return mwidth;
}

double ImageFile::height() const
{

    return mheight;
}
} 

2、ImageFile.h:

#ifndef ImageFile_H
#define ImageFile_H



namespace blink {

class  ImageFile  {
public:
    static ImageFile* create(const String& path)
    {
        FILE* fS;
        fS =fopen(path.utf8().data(),"r");
        if(fS !=NULL)
        {   
            int i;
            int iLen = path.length() ;
            int iPos = path.reverseFind('.');
            if (iPos <= 0)
            {
                return NULL;
            }
            String name=path.substring(iPos + 1, iLen);
            char s1[10];
            char s2[]="jpg";
            char s3[]="bmp";
            char s4[]="gif";
            char s5[]="png";
            char s6[]="jpeg";
            for(i=0;i<name.length();i++)
                s1[i] = name[i];
            s1[i] = '';
            if(strncmp(s1,s2,3)==0 || strncmp(s1,s3,3)==0 || strncmp(s1,s4,3)==0 || strncmp(s1,s5,3)==0|| strncmp(s1,s6,4)==0) 
                return new NGBImageFile(path);     //路径正确且图片文件格式是以上四种，创建文件对象
            else
                return NULL;       
        }
          return NULL;
    }

    String type() const;
    String location() const;
    String fileName() const;
    double width() const;
    double height() const;

private:
    ImageFile(const String& path);
    char* src;
    String mpath;
    String mtype;
    double mwidth;
    double mheight;
};

} // namespace blink

#endif // ImageFile_H