const void*p,char *p1,p1=*(char **)p

const void* p 是一个指向常量的指针，它可以向任何类型的数据，但不能通过该指针修改所指向的数据。

char* p1 是一个指向字符型数据的指针。

p1 = *(char**)p 的含义是将 p 强制转换为 char** 类型的指针，然后取出该指针指向的值，并将其赋给 p1。

这段代码的作用是将 p 指向的地址转为 char** 类型的指针，然后取出该指针指向的值，并将其赋给 p1。

相关问题

char *str(char *p1, const char *p2)传入这个函数的p1参数，会改变实参的值么

根据提供的引用内容，函数形参`char *str(char *p1, const char *p2)`中的`p1`参数是一个指向`char`类型的指针变量。当将实参传递给这个函数时，可以通过`p1`指针来修改实参的值。因此，传入这个函数的`p1`参数会改变实参的值。

范例：<<引用：#include <iostream> using namespace std; void changeValue(char *p) { *p = 'Y'; } int main() { char str[] = "Hello"; cout << "Before change: " << str << endl; changeValue(str); cout << "After change: " << str << endl; return 0; }>>

#include <iostream>
using namespace std;

void changeValue(char *p) {
    *p = 'Y';
}

int main() {
    char str[] = "Hello";
    cout << "Before change: " << str << endl;
    changeValue(str);
    cout << "After change: " << str << endl;
    return 0;
}

输出：

Before change: Hello
After change: Yello

void Zoom(const char *filename,double lx,double ly){ FILE *fp = fopen(filename,"rb"); if (fp == NULL) printf("Error"); BITMAPFILEHEADER fileHead; fread(&fileHead, sizeof(BITMAPFILEHEADER), 1, fp); BITMAPINFOHEADER infoHead; fread(&infoHead, sizeof(BITMAPINFOHEADER), 1, fp); int width = infoHead.biWidth; int height = infoHead.biHeight; int biCount = infoHead.biBitCount; RGBQUAD *pColorTable; int pColorTableSize = 0; pColorTable = new RGBQUAD[256]; fread(pColorTable, sizeof(RGBQUAD), 256, fp); pColorTableSize = 1024; unsigned char *pBmpBuf; int lineByte = (width*biCount / 8 + 3) / 4 * 4; pBmpBuf = new unsigned char[lineByte*height]; fread(pBmpBuf, lineByte*height, 1, fp); fclose(fp); int dstWidth = round(double(lx*width)); int dstHeight = round(double(ly*height)); int lineByte2 = (dstWidth*biCount / 8 + 3) / 4 * 4; unsigned char*pBmpBuf2; pBmpBuf2 = new unsigned char[lineByte2*dstHeight]; for (int i = 0; i < dstHeight; ++i){ for (int j = 0; j < dstWidth; ++j){ unsigned char *p; p = (unsigned char *)(pBmpBuf2 + lineByte2*i + j); (*p) = 255; } } int x = 0; int y = 0; for (int i = 0; i < height; ++i){ for (int j = 0; j < width; ++j){ unsigned char *p1, *p2; x = round(double(lx*j)); y = round(double(ly*i)); p1 = (unsigned char *)(pBmpBuf + i*lineByte + j); p2 = (unsigned char *)(pBmpBuf2 + y*lineByte2 + x); (*p2) = (*p1); } }

这段代码是一个图像缩放的函数，下面是对代码的中文注释：

// 将指定文件中的图像进行缩放后保存
// 参数filename为图像文件名，lx和ly为横向和纵向的缩放比例
void Zoom(const char *filename, double lx, double ly){                           
    FILE *fp = fopen(filename,"rb");
	if (fp == NULL)
		printf("Error");
 
	// 读取位图文件头和位图信息头
	BITMAPFILEHEADER fileHead;
	fread(&fileHead, sizeof(BITMAPFILEHEADER), 1, fp);
	BITMAPINFOHEADER infoHead;
	fread(&infoHead, sizeof(BITMAPINFOHEADER), 1, fp);
 
	// 获取图像的宽度、高度和颜色位数
	int width = infoHead.biWidth;
	int height = infoHead.biHeight;
	int biCount = infoHead.biBitCount;
 
	RGBQUAD *pColorTable;
	int pColorTableSize = 0;
 
	// 读取调色板数据
	pColorTable = new RGBQUAD[256];
	fread(pColorTable, sizeof(RGBQUAD), 256, fp);
	pColorTableSize = 1024;
 
	// 读取图像数据
	unsigned char *pBmpBuf;
	int lineByte = (width * biCount / 8 + 3) / 4 * 4;
	pBmpBuf = new unsigned char[lineByte * height];
	fread(pBmpBuf, lineByte * height, 1, fp);
	fclose(fp);
 
	// 计算缩放后的图像宽度和高度，并计算缩放后的每行字节数
	int dstWidth = round(double(lx * width));
	int dstHeight = round(double(ly * height));
	int lineByte2 = (dstWidth * biCount / 8 + 3) / 4 * 4;
	
	// 创建缩放后的图像数据缓冲区，并初始化为白色
	unsigned char *pBmpBuf2;
	pBmpBuf2 = new unsigned char[lineByte2 * dstHeight];
	for (int i = 0; i < dstHeight; ++i){
		for (int j = 0; j < dstWidth; ++j){
			unsigned char *p;
			p = (unsigned char *)(pBmpBuf2 + lineByte2 * i + j);
			(*p) = 255;
		}
	}
 
	// 对每个像素进行缩放处理
	int x = 0;
	int y = 0;
	for (int i = 0; i < height; ++i){
		for (int j = 0; j < width; ++j){
			unsigned char *p1, *p2;
			x = round(double(lx * j));
			y = round(double(ly * i));
			p1 = (unsigned char *)(pBmpBuf + i * lineByte + j);
			p2 = (unsigned char *)(pBmpBuf2 + y * lineByte2 + x);
			(*p2) = (*p1);
		}
	}
	
	// 将缩放后的图像数据保存到新文件中
	FILE *fp2 = fopen("zoomed.bmp", "wb");
	if (fp2 == NULL)
		printf("Error");
	fwrite(&fileHead, sizeof(BITMAPFILEHEADER), 1, fp2);
	fwrite(&infoHead, sizeof(BITMAPINFOHEADER), 1, fp2);
	fwrite(pColorTable, sizeof(RGBQUAD), 256, fp2);
	fwrite(pBmpBuf2, lineByte2 * dstHeight, 1, fp2);
	fclose(fp2);
 
	// 释放内存
	delete[] pColorTable;
	delete[] pBmpBuf;
	delete[] pBmpBuf2;
}

希望这些注释能帮助你理解代码的功能和实现过程。如果还有其他问题，请随时提问。