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 -

lee_鹿游原

820人浏览 · 2015-01-16 11:55:41

lee_鹿游原 · 2015-01-16 11:55:41 发布

/***

*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

[csharp]view plaincopy 
   
 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;  
 }   