并保存缩放后的文件，如何修改下列代码
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;
#pragma pack(1)//结构体中各成员按1字节对齐
struct BITMAPFILEHEADER//定义一个存储头文件数据结构体
{
unsigned short bfType; // 保存文件类型。'BM'
unsigned long bfSize; //位图文件总字节数
unsigned short bfReserved1; //位图文件保留字段，必须为0
unsigned short bfReserved2; //位图文件保留字段，必须为0
unsigned long bfOffBits; //RGB数据偏移地址，位图数据起始位置
};
struct BITMAPINFOHEADER//定义一个存储位图信息的结构体
{
unsigned long biSize; //本结构占用字节数
unsigned long biWidth; //位图像素宽度
unsigned long biHeight; //位图像素高度
unsigned short biPlanes; // bmp图片的平面数量，为1
unsigned short biBitCount; //每个像素所占的位数
unsigned long biCompression; //位图压缩类型，不压缩(为0)
unsigned long biSizeImage; //位图图像数据所占字节数
unsigned long biXPelsPerMeter; //位图水平分辨率，每米像素数
unsigned long biYPelsPerMeter; //位图垂直分辨率，每米像素数
unsigned long biClrUsed; //位图实际使用的颜色表中的颜色数
unsigned long biClrImportant; //位图显示过程中重要的颜色数
};
//zoom函数用于缩放，BITMAPFILEHEADER head, BITMAPINFOHEADER info为原图像头信息,缩放倍数为2，char字符串类型指针变量
void zoom(BITMAPFILEHEADER head, BITMAPINFOHEADER info, char *input, char *output, double rate)
{//r：打开文件仅供读取，w:打开文件仅供写入，b：二进制
FILE *fr = fopen(input, "rb");
FILE *fw = fopen(output, "wb");
//若读取不成功
if (fr == NULL || fw == NULL)
{
printf("图片错误\n");
return;
}
//读取原图像的头信息
fread(&head, sizeof(BITMAPFILEHEADER), 1, fr);
fread(&info, sizeof(BITMAPINFOHEADER), 1, fr);
unsigned int old_Width = info.biWidth;//获取原图像的宽信息
unsigned int old_height = info.biHeight;//获取原图像的高信息
unsigned char *old_data = (unsigned char *)malloc(old_Width * old_height * 3);//获取原图像的位图数据
////定位到图像数据位置
fseek(fr, 54, SEEK_SET);
fread(old_data, old_Width * old_height * 3, 1, fr);
//修改原图像的宽高
unsigned int new_Width, new_Height;
new_Width = (int)(rate * old_Width);//新宽等于倍数乘原宽
new_Height = (int)(rate * old_height);//新高等于倍数乘原高
//修改头信息
head.bfSize = new_Width * new_Height * 3 + 54;
info.biWidth = new_Width;
info.biHeight = new_Height;
//将修改后的头信息写进新图像
fwrite(&head, sizeof(BITMAPFILEHEADER), 1, fw);
fwrite(&info, sizeof(BITMAPINFOHEADER), 1, fw);
//缩放数据
int i = 0, j = 0;
unsigned long X, Y;
unsigned char *pd;
unsigned char *ps;
unsigned char *new_data = (unsigned char *)malloc(new_Width * new_Height * 3);
for (i = 0; i < new_Height; i++)
{
Y = i / rate;
pd = new_data + i * new_Width * 3;
ps = old_data + Y * old_Width * 3;
for (j = 0; j < new_Width; j++)
{
X = j / rate;
memcpy(pd + j * 3, ps + X * 3, 3);//拷贝数据
}
}
//新文件数据定位
fseek(fw, 54, SEEK_SET);
fwrite(new_data, new_Width * new_Height * 3, 1, fw);
printf("已成功缩放图像\n");
//释放空间
free(new_data);
free(old_data);
//关闭fr,fw
fclose(fr);
fclose(fw);
}
int main(int argc, char *argv[])
{
//申明存储图像数据的结构体
BITMAPFILEHEADER old_head;
BITMAPINFOHEADER old_info;
//初始化结构体变量
memset(&old_head, 0, sizeof(BITMAPFILEHEADER));
memset(&old_info, 0, sizeof(BITMAPINFOHEADER));
//将缩放比例转化为double类型
double rate = atof(argv[2]) / 100.0;
zoom(old_head, old_info, argv[1], argv[3], rate);
return 0;
}
