Simple implementation of several string library functions in c

Simple implementation of several string library functions in c

 #include<stdio.h>#include<stdlib.h>#include<string.h>#include<malloc.h>int fun1(char *p){  int len=0;while(*p!=0){len++;p++;}  return len;}int fun2(const char *s){   const char *p=s;   while(*p++);    return p-s-1;}/*************pabcdes-----s1234567    *************/int fun3(const char *s){ if(*s==0)return 0;  else return(1+fun3(s+1));}void *fun4(char *d,const char*s,int n){//assert(d);assert(s); char *ret=d;while(*d){d++;}//d move to \0while(n)       {*d++=*s++;n--;}//\0\0\0 turn to abcde....return ret; }void *fun5(  char *d,  char *s){  char *ret=NULL;  while(*d)  {    while(*s){if(*d==*s){d++;s++;}else break;}    if(*s==0) return ret;    else {d++;ret=d;}  }}//44void *fun6(  char *s1,  char *s2){char *pstr=s1;char *p1=NULL;char *p2=NULL;  while(*pstr)  {  p1=pstr;p2=s2;    while((*p1)&&*p1==*p2){p1++;p2++;if(*p2==0)return pstr;}     pstr++;      }return 0;}char *fun7(char *d,const char *s){char *ret=d;while(*d++=*s++);return ret;}/*******s1<--s2*******/int fun8(const char* s1,const char *s2){while(*s1==*s2){if(*s1==0)return 0; s1++;s2++;} return (*s1-*s2);}/*******s1>s2  return  1 2 3....*******/void *fun9(void *d,const void *s,int size){void *ret=d;char *p1=(char *)d;char *p2=(char *)s;while(size--){*p1++;*p2++;}return ret;}void *fun10(void *d,const void *s,int size){void *ret=d;char *p1=(char *)d;char *p2=(char *)s;if(p1>p2&&p1<p2+size){while(size--){*(p1+size)=*(p2+size);}}else while(size--){*p1++=*p2++;}return ret;}void main(){char ss[]="abcde";char s1[]="abcde";char s2[]="abcde";char *p=ss; //printf("%d\n",strlen(p)); //printf("%d\n",fun1(p)); //printf("%d\n",fun2(p)); //  printf("%d\n",fun3(p));//   printf("%s\n",fun4(s1,s2,1));//have bug printf more about s2;//   printf("%s\n",fun6(s1,s2));//   printf("%s\n",fun7(s1,s2));//   printf("%d\n",fun8(s1,s2));printf("%s\n",fun9(s1,s2,5));printf("%s\n",fun10(s1,s2,5));}