初识openssl库之计算文件的md5值

openssl是密码学一个很重要的库，调用openssl库进行编程可以大大简化代码的复杂度，今天要介绍的是使用openssl库计算文件的md5值，代码如下：

#include <openssl/md5.h>
#pragma comment(lib, "libeay32.lib")
#pragma comment(lib, "ssleay32.lib")

void main()
{
	int i,blocklength;
	long int filelength;
	unsigned char ch[4096], s[64];
	char filepath[256];
	FILE* fp;
	puts("文件md5计算器 by 厄斐琉斯\n");
	while(true)
	{
		printf("请输入文件完整路径名:");
		scanf("%s", filepath);
		if((fp=fopen(filepath,"rb"))==NULL)
			printf("can't open the file\n");
		MD5_CTX m;
		MD5_Init(&m);
		fseek(fp,0L,SEEK_END);
		filelength=ftell(fp);
		fseek(fp,0L,SEEK_SET);
		blocklength = 4096;
		while(filelength > blocklength)
		{
			fread(ch,sizeof(unsigned char),blocklength,fp);
			MD5_Update(&m, ch, blocklength);
			filelength -= blocklength;
		}
		fread(ch,sizeof(unsigned char),filelength,fp);
		MD5_Update(&m, ch, filelength);
		MD5_Final(s, &m);
		printf("文件的md5值为:");
		for(i=0; i<16; i++)
			printf("%02X", s[i]);
		printf("\n\n");
	}
}

程序使用VC6.0环境编译运行