用字符指针实现函数strcat(s,t),将字符串t复制到字符串s的末端，并且返回字符串s的首地址，

不会。。。。。。。。。。。。

char *sss(char *s1, char *s2)
{

 while(*s1)

 {
    s1 ++;

 }

 while(*s1 ++ = *s2 ++);


 return s1;   
}

STRCAT()貌似是这样写的··不过，前面还得加个ASSERT();

VC源码：
char * __cdecl strcat (char * dst, const char * src)
{
char * cp = dst;
while( *cp )
cp++; /* find end of dst */
while( *cp++ = *src++ ) ; /* Copy src to end of dst */
return( dst ); /* return dst */
}

linux 下 glibc 2.9下

/* Append SRC onto DEST.  */
#define _HAVE_STRING_ARCH_strcat 1
#define strcat(dest, src) \
  (__extension__ (__builtin_constant_p (src)                      \
          ? __strcat_c ((dest), (src), strlen (src) + 1)          \
          : __strcat_g ((dest), (src))))

__STRING_INLINE char *__strcat_c (char *__dest, __const char __src[],
                  size_t __srclen);

__STRING_INLINE char *
__strcat_c (char *__dest, __const char __src[], size_t __srclen)
{
#ifdef __i686__
  register unsigned long int __d0;
  register char *__tmp;
  __asm__ __volatile__           ////内联汇编
    ("repne; scasb"
     : "=D" (__tmp), "=&c" (__d0),
       "=m" ( *(struct { char __x[0xfffffff]; } *)__dest)
     : "0" (__dest), "1" (0xffffffff), "a" (0),
       "m" ( *(struct { __extension__ char __x[__srclen]; } *)__src)
     : "cc");
  --__tmp;
#else
  register char *__tmp = __dest - 1;
  __asm__ __volatile__
    ("1:\n\t"
     "incl    %0\n\t"
     "cmpb    $0,(%0)\n\t"
     "jne    1b\n"
     : "=r" (__tmp),
       "=m" ( *(struct { char __x[0xfffffff]; } *)__dest)
     : "0" (__tmp),
       "m" ( *(struct { __extension__ char __x[__srclen]; } *)__src)
     : "cc");
#endif
  (void) memcpy (__tmp, __src, __srclen);
  return __dest;
}

__STRING_INLINE char *__strcat_g (char *__dest, __const char *__src);

__STRING_INLINE char *
__strcat_g (char *__dest, __const char *__src)
{
  register char *__tmp = __dest - 1;
  register char __dummy;
  __asm__ __volatile__         
    ("1:\n\t"
     "incl    %1\n\t"
     "cmpb    $0,(%1)\n\t"
     "jne    1b\n"
     "2:\n\t"
     "movb    (%2),%b0\n\t"
     "incl    %2\n\t"
     "movb    %b0,(%1)\n\t"
     "incl    %1\n\t"
     "testb    %b0,%b0\n\t"
     "jne    2b\n"
     : "=&q" (__dummy), "=&r" (__tmp), "=&r" (__src),
       "=m" ( *(struct { char __x[0xfffffff]; } *)__dest)
     : "1"  (__tmp), "2"  (__src),
       "m" ( *(struct { char __x[0xfffffff]; } *)__src)
     : "memory", "cc");
  return __dest;
}

呃，好复杂。。。