微软strcpy,strcat和strcmp的实现源代码 itoa atoi
/****char *strcpy(dst, src) - copy one string over another**Purpose:* Copies the string src into the spot specified by* dest; assumes enough room.**Entry:* char * dst -
/***
*char *strcpy(dst, src) - copy one string over another
*
*Purpose:
* Copies the string src into the spot specified by
* dest; assumes enough room.
*
*Entry:
* char * dst - string over which "src" is to be copied
* const char * src - string to be copied over "dst"
*
*Exit:
* The address of "dst"
*
*Exceptions:
*******************************************************************************/
char* strcpy(char * dst, const char * src)
{
char * cp = dst;
while( *cp++ = *src++ )
; /* Copy src over dst */
return( dst );
}
/***
*char *strcat(dst, src) - concatenate (append) one string to another
*
*Purpose:
* Concatenates src onto the end of dest. Assumes enough
* space in dest.
*
*Entry:
* char *dst - string to which "src" is to be appended
* const char *src - string to be appended to the end of "dst"
*
*Exit:
* The address of "dst"
*
*Exceptions:
*
*******************************************************************************/
Char* 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 */
}
/***
*strcmp - compare two strings, returning less than, equal to, or greater than
*
*Purpose:
* STRCMP compares two strings and returns an integer
* to indicate whether the first is less than the second, the two are
* equal, or whether the first is greater than the second.
*
* Comparison is done byte by byte on an UNSIGNED basis, which is to
* say that Null (0) is less than any other character (1-255).
*
*Entry:
* const char * src - string for left-hand side of comparison
* const char * dst - string for right-hand side of comparison
*
*Exit:
* returns -1 if src < dst
* returns 0 if src == dst
* returns +1 if src > dst
*
*Exceptions:
*
*******************************************************************************/
int strcmp ( const char* src, const char* dst )
{
int ret = 0 ;
while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
++src, ++dst;
if ( ret < 0 )
ret = -1 ;
else if ( ret > 0 )
ret = 1 ;
return( ret );
}
itoa atoi
- void itoa(int num,char str[] )
- {
- int sign = num,i = 0,j = 0;
- char temp[11];
- if(sign<0)//判断是否是一个负数
- {
- num = -num;
- }
- do
- {
- temp[i] = num%10 + '0';
- num/=10;
- i++;
- }while(num>0);
- if(sign<0)
- {
- temp[i++] = '-';//对于负数,要加以负号
- }
- temp[i] = '\0';
- i--;
- while(i>=0)//反向操作
- {
- str[j] = temp[i];
- j++;
- i--;
- }
- str[j] = '\0';
- }
- int atoi(char s[])
- {
- int i = 0,sum = 0,sign; //输入的数前面可能还有空格或制表符应加判断
- while(' '==s[i]||'\t'==s[i])
- {
- i++;
- }
- sign = ('-'==s[i])?-1:1;
- if('-'==s[i]||'+'==s[i])
- {
- i++;
- }
- while(s[i]!='\0')
- {
- sum = s[i]-'0'+sum*10;
- i++;
- }
- return sign*sum;
- }
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