字符串库函数总结

1、strcat

char* strcat1(char*dst,char *src)
       {
           char *addr=dst;
           while(*addr!='')
               addr++;
           while(*addr=*src)
               {
                  src++;addr++;
               }
           return addr;
       }

2、strcmp

int strcmp1(char*str1,char* str2 )
    {
      while(*str1&&*str2&&*str1==*str2)
          {
             str1++;
             str2++;
          }
          return *str1-*str2;
    }

3、strcpy

char *strcpy1(char* dst,char* src)
    {
        char * addr= dst;
        while(*src)
            {
                *addr++=*src++;
            }
        *addr='';
        return addr;
    }

4、strstr

int strstr1(char* string,char*substring)
    {
    int i,j;
       if(string==NULL||substring==NULL)
           return -1;
       int lenstr=strlen(string);
       int lensub=strlen(substring);
       if(lenstr<lensub) return -1;
       for( i=0;i<lenstr-lensub;i++)
           {
           for(j=0;j<lensub;j++)
               {
                  if(string[i+j]!=substring[j])
                      break;
               }
              if(j==lensub)
                  return i+1;
           }
       return -1;
    }