int strlen(const char* str)

{

char* p = str;

while(*(str++));

return (str-1-p);

}


char* strstr(const char* str, const char* c)

{

char* p;

char* t;

while(*(p=str++)) {

for(t = c; *t, !(*p-*t)   ; p++, t++);

if(!t) return --str;

}

return null;

}






char* strcat(char* str1, const char* str2)

{

char* p  = str1;

while(*(str1++));

str1--;

while(*(str1++) = *(str2++));

return p;

}





int strcmp(const char* str1, const char* str2)

{

while(!(ret = *(str1++)-*(str2++)) && *str2 );


if(ret<0)

return -1;

else if(ret>0)

return 1;

else

return 0;

}






char* strcpy(char* str1, const char* str2)

{

char *p = str1;

while(*(str1++) = *(str2++));

return p;

}




내가 짠건 아니고 visualstudio include에 있는 내용