c++ 头文件(或者string.h)中的常见函数的实现！
下面是一些
下面贴代码！！！
// 此文件可以命名为"cstring.h" （这与标准库的并不冲突）
// vs2012 调试通过
#pragma once
#ifndef MYSTD_CSTRING_H
#define MYSTD_CSTRING_H
#include // assert
#include // std::size_t
#define MYSTD_BEGIN namespace mystd{
#define MYSTD_END }
#ifdef __cplusplus
//封装于名字空间mystd中
MYSTD_BEGIN
typedef std::size_t size_type;
typedef unsigned char UCHAR;
// C语言版本，void * memchr(const void *,int,size_type);
inline const void* memchr(const void *pointer,int val, size_type num)
{
assert(pointer != 0);
UCHAR *ptr = (UCHAR*)pointer;
for(size_type i = 0; i < num; ++i)
{
if(*ptr == val)
break;
++ptr;
}
return ptr;
}
inline void* memchr(void *pointer, int val,size_type num) //c++重载
{
assert(pointer != 0);
return (void*)mystd::memchr((const void*)pointer,val,num); // 转调
}
inline size_type strlen(const char *str)
{
assert(str != 0);
size_type count = 0;
while(*str++)
++count;
return count;
}
inline void* memmove(void *destination,const void *source, size_type num)
{ // 对于memmove函数的实现，c++之父在《c++ 程序设计语言》（十周年中文纪念版第16章开篇）
//就说过，此函数无法由c++语言本身达到最优实现，实际应用时还是用标准库吧！
assert(destination != 0 && source != 0);
if(destination == source || num == 0)
return destination;
UCHAR *des = (UCHAR*)destination;
const UCHAR *src = (UCHAR*)source;
if(des < src || des >= src + num)
{
while(num--)
*des++ = *src++;
return destination;
}
des += num;
src += num;
while(num--) // 倒序复制
*--des = *--src;
return destination;
}
inline void* memcpy(void *destination,const void *source, size_type num)
{
assert(destination != 0 && source != 0);
return mystd::memmove(destination,source,num);
}
inline int memcmp(const void *pointer_1,const void *pointer_2,size_type num)
{
assert(pointer_1 != 0 && pointer_2 != 0);
const UCHAR *ptr_1 = (UCHAR*)pointer_1;
const UCHAR *ptr_2 = (UCHAR*)pointer_2;
while(num-- && *ptr_1 == *ptr_2)
++ptr_1,++ptr_2;
if(num == size_type(-1))
return 0;
else
return *ptr_1 - *ptr_2;
}
inline void* memset(void *pointer,int val,size_type num)
{
assert(pointer != 0);
UCHAR *ptr = (UCHAR*)pointer;
while(num--)
*ptr++ = val;
return pointer;
}
inline char* strcat(char *destination,const char *source)
{
assert(destination != 0 && source != 0);
char *ptr = destination + mystd::strlen(destination);
while(*ptr++ = *source++);
return destination;
}
inline char *strncat(char *destination,const char *source,size_type num)
{
assert(destination != 0 && source != 0);
char *ptr = destination + mystd::strlen(destination);
while(num-- && *source)
*ptr++ = *source++;
*ptr = 0; // null-character 复制
return destination;
}
inline char *strcpy(char *destination,const char *source)
{
assert(destination != 0 && source != 0);
char *des = destination;
while(*des++ = *source++);
return destination; // null-character被复制
}
inline char *strncpy(char *destination,const char *source,size_type num)
{
assert(destination != 0 && source != 0);
char *des = destination;
while(num--)
*des++ = *source++;
return destination; // null-character可能没有被复制
}
inline int strcmp(const char *str1,const char *str2)
{
assert(str1 != 0 && str2 != 0);
while(*str1 && *str1 == *str2)
++str1, ++str2;
return *str1 - *str2;
}
inline int strncmp(const char *str1,const char *str2,size_type num)
{
assert(str1 != 0 && str2 != 0);
while(num-- && *str1 && *str1 == *str2)
++str1, ++str2;
if(num == size_type(-1)) // 包含了num == 0的情况
return 0;
else
return *str1 - *str2;
}
//C语言只有一个版本 char* strchr(const char *, int);
inline const char* strchr(const char *str,int character)
{
assert(str != 0);
// 语言标准规定character 为int,这里转换一下
const char chr = *(char*)&character;
while(*str && *str != chr)
++str;
if(*str)
return str;
else
return 0;
}
inline char* strchr(char *str,int character) //c++重载
{
assert(str != 0);
return (char*)mystd::strchr((const char*)str,character);
}
inline const char* strrchr(const char *str,int character)
{ //这里的character 可能包括null-character
assert(str != 0);
// 语言标准规定character 为int,这里转换一下
const char chr = *(char*)&character;
// const char chr = (char)character; // 也可以这样
size_type len = mystd::strlen(str);
const char *ptr = str + len;
if(chr == 0)
return ptr;
--ptr;
while(len--)
if(*ptr == chr)
return ptr;
else
--ptr;
return 0; //无匹配的字符
}
inline char* strrchr(char *str,int character)
{
assert(str != 0);
return (char*)mystd::strrchr((const char*)str,character); // 转调
}
//c语言版本char* strstr(const char *,const char*);
inline const char* strstr(const char* str1,const char* str2)
{
assert(str1 != 0 && str2 != 0);
size_type len_1 = mystd::strlen(str1);
size_type len_2 = mystd::strlen(str2);
if(len_1 < len_2)
return 0;
const char *search_last = str1 + (len_1 - len_2);
while(str1 <= search_last)
{
if(mystd::strncmp(str1,str2,len_2) == 0)
return str1;
else
++str1;
}
return 0;
}
inline char* strstr(char *str1,const char *str2) //c++重载
{
assert(str1 != 0 && str2 != 0);
return (char*)mystd::strstr((const char*)str1,str2);
}
inline bool is_inside(const char *str,char chr) // 辅助函数，内部使用
{
assert(str != 0);
while(*str)
{
if(*str == chr)
return true;
else
++str;
}
return false;
}
inline size_type strspn(const char* str1,const char *str2)
{
assert(str1 != 0 && str2 != 0);
size_type count = 0;
while(*str1 && is_inside(str2,*str1))
++count, ++str1;
return count;
}
inline size_type strcspn(const char* str1,const char *str2)
{
assert(str1 != 0 && str2 != 0);
size_type count = 0;
while(*str1 && !is_inside(str2,*str1))
++count, ++str1;
return count;
}
// c语言版本char* strpbrk(const char *,const char *);
inline const char* strpbrk(const char *str1,const char *str2)
{
assert(str1 != 0 && str2 != 0);
while(*str1 && !is_inside(str2,*str1))
++str1;
if(*str1 == 0)
return 0;
else
return str1;
}
inline char* strpbrk(char *str1,const char *str2) //c++重载
{
assert(str1 != 0 && str2 != 0);
return (char*)strpbrk((const char*)str1,str2); //转调
}
MYSTD_END // end of namespace mystd
#endif // __cplusplus
#endif // MYSTD_CSTRING_H
下面是一个简单的测试程序：
#include
#include"cstring.h" //自写版本
#include // 标准库
#define STD mystd // 更改为std可以调用标准库版本
using std::cout;
using std::endl;
int main()
{
char buf[100];
const char* str = "hello world";
STD::memset(buf,0,sizeof(buf));
STD::memcpy(buf,str,STD::strlen(str));
cout< 本人在vs2012中测试通过。