对字符串进行位运算，用C语言怎么写？

[jdgdf566]

一个长度为12个字节的字符串"abcdefghijkl"，把这段8*12bit长度的数据的偶数位(二进制位)变成0，即进行位运算。因为逐个字节运算速度慢，我想每次运算4个字节(即32bit)。使用循环，每次运算4个字节，当然是循环3次。我的办法是，把每4个字节看作一个long整型数据，位运算之后，使用memcpy()函数把结果拷贝到目标指针上。这样循环3次。下面写的代码，得不到正确的结果。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/**
* 打印数值二进制值的函数
**/
void printNumber(unsigned long n, int length)
{
    char str[length];
    itoa(n,str,2);//2即是代表转换为2进制
    //补足前面的0
    int count = length - strlen(str);
    int i;
    for(i=0; i<count; ++i)
    {
        printf("0");
    }
    //
    printf("%s",str);
}

/**
* 打印字符串二进制值的函数
**/
void printString(char *s)
{
    char c;
    unsigned long j=(unsigned long)s + strlen(s);
    for(; (unsigned long)s<j; s++)
    {
        c = *s;
        printNumber((unsigned long)c, 8);
    }
}

/**
* 主函数
*/
int main(int argc, char *argv[])
{
	unsigned int length= 8;
    char src[8] = "abcdefgh";
    char dest[8] = "tttttttt";	//存放结果
    unsigned long* srcLong = src;
    unsigned long* destLong = dest;
    //
    unsigned long key1 = 0xaaaaaaaa;		//1010....
    unsigned long n;
    //
    printNumber(key1, 32);printNumber(key1, 32); puts(":key1");
    printString(src); puts(":src");
    //
    //unsigned long * endLong = src + 8;
	unsigned int count = length/4;
	unsigned int i;
    for(i=0; i<count; i++) //srcLong < endLong
    {
        n = (*srcLong) & key1;
        //printString((char*)&n);
        memcpy((void *)destLong, (void *)&n, 4);
        srcLong += 4;
		destLong +=4;
    }
	printString(dest); puts(":dest");


    return 0;
}

[zgl7903]

因为是long 指针，所以+1就可以了
srcLong++; //srcLong += 4;
destLong++; //destLong +=4;

还要留意长度不能被4整除的情况

[sghcpt]

楼主，可以试试下面代码~~只供参考。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/**
* 打印数值二进制值的函数
**/
void printNumber(unsigned long n, int length)
{
	char str[246] = { 0 };
	_itoa(n, str, 2);//2即是代表转换为2进制
	//补足前面的0
	int count = length - strlen(str);
	int i;
	for (i = 0; i<count; ++i)
	{
		printf("0");
	}
	//
	printf("%s", str);
}

/**
* 打印字符串二进制值的函数
**/
void printString(char *s)
{
	char c;
	size_t j = strlen(s);
	size_t i = 0;
	for (;  i < j; s++)
	{
		c = *s;
		printNumber((unsigned long)c, 8);
		++i;
	}
}

/**
* 主函数
*/
int main(int argc, char *argv[])
{
	unsigned int length = 8;
	char src[9] = "abcdefgh";
	char dest[9] = "tttttttt";	//存放结果
	unsigned long* srcLong = (unsigned long*)src;
	unsigned long* destLong = (unsigned long*)dest;
	//
	unsigned long key1 = 0xaaaaaaaa;		//1010....
	unsigned long n;
	//
	printNumber(key1, 32); puts(":key1");
	printString(src); puts(":src");
	

	unsigned int count = length / 4;
	unsigned int i;
	for (i = 0; i < count; i++) //srcLong < endLong
	{
		n = (*srcLong) & key1;
		memcpy((void *)destLong, (void *)&n, 4);
		srcLong += 1;
		destLong += 1;
	}
	printString(dest); puts(":dest");

	return 0;
}