字符串操作

#include "stdafx.h"
#include "stdio.h"
#include <cstring>

int main(int argc, char* argv[])
{
	//char d[] = "123";
	char s[] = "123456789";
	char d[] = "123";
	strcpy(d,s);
	printf("%s,\n%s",d,s);
	printf("Hello World!\n");
	return 0;
}

上述执行结果为：123456789，56789.分配的内存地址是连续内存。原来是123\0123456789\0,strcpy后变成了123456789\06789\0.如果把目标字串定义在前，源字符串定义在后，则产生运行期错误。访问到了不可预知的地址。
字符串拷贝函数实现

void stringcpy(char *to, const char *from){
	assert(to != NULL && from != NULL);
	while(*from != '\0'){
		*to++ = *from++;
	}
	*to = '\0';
}

int strcmp (const char * src, const char * dst)
{
        int ret = 0 ;

        while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *src)
                ++src, ++dst;

        if ( ret < 0 )
                ret = -1 ;
        else if ( ret > 0 )
                ret = 1 ;

        return( ret );
}

字符串比较

查找子字符串在母字符串出现的位置，返回地址值。

char * findsub(char * mother, char * son)
{
    for(int i = 0; i < strlen(mother); i++)
	{
		char * temp_mother = mother + i;
		char * temp_son = son;
		while( (* temp_mother) == (*temp_son) && ( (*temp_son) != '\0'))
		{
			temp_mother++;
			temp_son++;
		}
		if ( (*temp_son) == '\0')
		{
			return mother + i;	
		}
		
	}
	return NULL;
}

翻转单词：

void reverse_word()
{

	char a[] = "I love you";
	char b[] = "11";
	printf("strlen b is %d\n",strlen(b));//strlen不包含最后的'\0'结束符，
                                      //这点和sizeof 不一样。
	int end = strlen(a) - 1;
	int start = 0;
	while(start <= end)  //将整个字符串翻转，
	{
		char temp = a[start];
		a[start] = a[end];
		a[end] = temp;
		start++;
		end--;
	}
	printf("after reverse is %s\n",a);//再逐个单词翻转。
        start = 0;
	while(a[start] == ' ')
		start++;
	while(a[start] != '\0')
	{
	    int end = start;
		while(a[end] != ' ' && (a[end] != '\0'))  //找到第一个单词结束位置
			end++;
		end--;
		printf("end is %d\n",end);
		int tempend = end + 1;
		while(start <= end)
		{
			char temp = a[start];
		    a[start] = a[end];
		    a[end] = temp;
		    start++;
		    end--;
		}
		while(a[tempend] == ' ' && (a[tempend] != '\0'))
			tempend++;
		start = tempend;
	}
    printf("a is %s\n",a);
}