字符串库函数

#include <iostream>using namespace std;int strlenn(const char* str){int i=0;while (str[i]!=0) i++;return i;}int strcmp(const char* s1,const char* s2){int len1=strlenn(s1);int len2=strlenn(s2);for (int i=0;i<len1 && i<len2 ; ++i){if(s1[i]<s2[i]) return -1;if(s1[i]>s2[i]) return 1;}if(len1 < len2) return -1;if(len1 > len2) return 1;return 0;}int strcopy(char* s1,const char* s2){//int len1=sizeof(s1)/sizeof(s1[0]);int len2=strlenn(s2);//if(len1 < len2+1) return -1;for (int i=0;i<len2;i++){s1[i]=s2[i];}s1[len2]=0;return 0;}int struupr(char* s){int len=strlenn(s);for (int i=0;i<len;i++){if(s[i]>='a' && s[i]<='z')s[i]=s[i]+'A'-'a';}return 0;}int strcatt(char* s1,const char* s2){int len1=strlenn(s1);int len2=strlenn(s2);for (int i=len1;i<len1+len2;++i){s1[i] = s2[i-len1];}s1[len1+len2] = 0;return 0;}int main(){char* s1="hello world";cout<<strlenn(s1)<<endl;cout<< strcmp("aabb","aabc")<<endl;char buf[30];strcopy(buf,"hello");strcatt(buf,s1);cout<<buf<<endl;struupr(buf);cout<<buf<<endl;}