strcpy、strcmp和memcpy 函数实现

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#include <iostream>#include <assert.h>using namespace std;//字符串拷贝函数char* strcpy(char *des,char *src){assert( des!=NULL && src!=NULL );char *address = des;while( (*des+ += *src++) != '\0' ) NULL;return address;}//字符串比较函数int strcmp(char *str1,char *str2){while( *str1!='\0' && *str1==*str2){++str1; ++str2;}if(*str1>*str2) return 1;if(*str1<*str2) return -1;return 0;}//内存拷贝函数（考虑内存重叠）void* memcpy(void *des,void *src,size_t n){assert( des!=NULL && src!=NULL && n>0 );char *pdes = (char*)des;char *psrc = (char*)src;if( psrc<pdes && psrc+n>pdes ){while(n--!=0)pdes[n] = psrc[n];}else{for(size_t i=0;i!=n;++i)pdes[i] = psrc[i];}return des;}int main(){char des[10] = "9999";char src[] = "123";cout << des << ", " << src << " " << "字符串比较结果: " << strcmp(des,src) << endl;cout << "字符串拷贝：" << endl;//strcpy(des,src);memcpy(src+1,src,2);//memcpy(src,src+1,2);cout << "src: " << src << '\n' << "des: " << des << endl;}

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