手动实现的C语言string.h 头文件的字符串函数

研究C语言，首先要明白其库函数…

001#include<stdio.h>

002char* strcpy(char* dest,const char* src);  //字符串拷贝

003char* strcat(char* dest,const char* src);  //字符串连接,返回dest字符串

004char* strncat(char* dest, const char* src, int size);//把src前n个字符串连接到dest,返回dest字符串

005int   strcmp(const char* src1,const char* src2);  //字符串比较  返回值: 1:> 0:= -1<

006int   strncmp(const char* src,const char* dst,int size);  //dst前n个字符和src比较返回值: 1:>  0:=  -1<

007int   strlen(const char* src);  //返回字符串长度

008char* strchr(const char* src, int ch); //字符ch在字符串第一次出现的位置,返回出现字符ch位置开始到字符串结束位置的指针

009char* strrchr(const char* src, int ch); //字符ch在字符串最后一次出现的位置,返回出现字符ch位置开始到字符串结束位置的指针

010char* strstr(const char* src, const char* sub); //字符串sub在字符串第一次出现的位置,返回出现字符串sub位置开始到字符串结束位置的指针

011//memery copy operate function==================//

012void* memcpy(void* dest,const void* src,unsigned int size); //把src的内容拷到dest内存里去,并返回dest指向的内存地址

013void* memset(void* dst, int ch, unsigned int size); //把dst内存中的size大小用使用ch来初始化,并返回dest指向的内存地址

014int   memcmp(const void* src1, const void* src2, unsigned int size); //比较内存中src1与src2中的前size 个字符是否相等,1:>  0:=  -1<  (see strncmp(const char*,const char*,unsigned int))

015void* memchr(const void* dst, int ch, unsigned int size); //在内存中的某一范围内,查找特定的字符ch,并返回指向ch的指针

016void* memmove(void* dst, const void* src, unsigned int size); //memmove()与memcpy()一样都是用来拷贝src所指的内存内容前n个字节到dest所指的地址上。不同的是，当src和dest所指的内存区域重叠时，memmove()仍然可以正确的处理，不过执行效率上会比使用memcpy()略慢些.返回指向dest的指针

017//memery copy operate function==================//

018int main()

019{

020// printf("the string len=%d/n",strlen("helloWorld")); 

021// char dest[20];

022// printf("the string is=%s/n",strcpy(dest,"helloWorld"));

023// char dest[30]="hello--";

024// printf("after connect sub string is=%s/n",strcat(dest,"world"));

025// char dest[30]="hello--";

026// printf("after connect sub string is=%s/n",strncat(dest,"world_programe",4));

027// printf("the string compare result is=%d/n",strcmp("hello","aello"));

028// printf("the string compare result is=%d/n",strncmp("hello","hello_good",5));

029// printf("the char appear position is=%s/n",strchr("hello-r-es-d",'-'));

030// printf("the char appear position is=%s/n",strrchr("hel*lo-r*-e*s-d",'*'));

031// printf("the sub string is=%s/n",strstr("hello_world","lo"));

032char dest[20];

033// printf("the sub string is=%s/n",memcpy(dest,"hello..111",sizeof(dest)));

034printf("the sub string is=%s/n",memset(dest,'0',sizeof(dest)));

035return 0;

036}

037//=========================================================//

038int  strlen(const char* src)

039{

040const char* p=src;

041

while(*p!='/0')

{

  p++;

} 

042return p-src;

043}

044//=========================================================//

045char* strcpy(char* dest,const char* src)

046{

047if(dest&&src)

048{

049int i=0;

050while((*(dest+i)=*(src+i))!='/0') i++;

051*(dest+i)='/0';

052// return dest;

053}

054return dest;

055}

//微软源码

char * __cdecl strcpy(char * dst, const char * src)
{
        char * cp = dst;

        while( *cp++ = *src++ )
                ;               /* Copy src over dst */

        return( dst );
}

//

056//=========================================================//

057char* strcat(char* dest,const char* src)

058{

059if(dest&&src)

060{

061int len=strlen(dest);

062// printf("len=%d/n",len);

063int i=0;

064while((*(dest+len+i)=*(src+i))!='/0') i++;

065*(dest+len+i)='/0';

066}

067return dest;

068}

069//=========================================================//

070char* strncat(char* dest, const char* src, int size)

071{

072if(dest&&src)

073{

074int len=strlen(dest);

075int i=0;

076while((i<size)&&((*(dest+len+i)=*(src+i))!='/0')) i++;

077}

078return dest;

079}

080//=========================================================//

081int strcmp(const char* src1,const char* src2)

082{

083int equal;

084int i=0;

085while(!(equal=*(unsigned char*)(src1+i)-*(unsigned char*)(src2+i))&&(*(src1+i))&&(*(src2+i)))

086i++;

087if(equal<0) return -1;

088else if(equal>0) return 1;

089else return 0;

090}

int strcmp(char *str1,str2)
{
char *p1,*p2;
p1=str1;
p2=str2;
while(*p2 && *p1)
if(*(p1++)- *(p2++) )return *(p1++)- *(p2++) ;
return 0;

}

091//=================比较两个字符串前size 个字符串是否相等==========================//

092int strncmp(const char* src1,const char* src2,int size)

093{

094int equal;

095int i=0;

096while((i<size)&&!(equal=*(unsigned char*)(src1+i)-*(unsigned char*)(src2+i))&&(*(src1+i))&&(*(src2+i)))

097i++;

098if(equal<0) return -1;

099else if(equal>0) return 1;

100else return 0;

101}

102//=========================================================//

103char* strchr(const char* src, int ch)

104{

105int i=0;

106while(*(src+i)&&(*(src+i)!=ch)) i++;

107return (char*)(src+i);

108}

109//=========================================================//

110char* strrchr(const char* src, int ch)

111{

112int len=strlen(src);

113int i=0;

114while(i<len&&(*(src+len-i)!=ch)) i++;

115return (char*)(src+(len-i));

116}

117//=========================================================//

118char* strstr(const char* src, const char* sub)

119{

120if(src&&sub)

121{

122int subLen=strlen(sub);

123int srcLen=strlen(src);

124int nomatch=1;

125int fds=srcLen-subLen+1;

126int i=0;

127if(fds>0) //find counts in the string

128while((nomatch=strncmp(src+i,sub,subLen))&&fds--)//把当前src的指针往后推,直到找到与sub指针相同为止

129i++;

130if(nomatch)

131return 0;

132else

133return (char*)(src+i);

134}

135return 0;

136}

137//====================memory operate=====================================//

138//====================memory operate=====================================//

139void* memcpy(void* dest,const void* src,unsigned int size)

140{

141if(dest&&src&&size>0)

142{

143int i=0;

144unsigned char* p=(unsigned char*)dest;

145unsigned char* q=(unsigned char*)src;

146while((i<size)&&(*(p+i)=*(q+i)))

147i++;

148return dest;

149}

150return 0;

151}

152//=========================================================//

153void* memset(void* dst, int ch, unsigned int size)

154{

155int i=0;

156unsigned char* p=(unsigned char*)dst;

157while((i<size)&&(*(p+i)=ch))

158i++;

159return dst;

160}

161//=========================================================//

162int  memcmp(const void* src1, const void* src2, unsigned int size)

163{

164}

165//=========================================================//

166void* memchr(const void* dst, int ch, unsigned int size)

167{

168}

169void* memmove(void* dst, const void* src, unsigned int count)

170{

171void * ret = dst;

172if (dst <= src || (char *)dst >= ((char *)src + count))

173{

174while (count--)

175{

176*(char *)dst = *(char *)src;

177dst = (char *)dst + 1;

178src = (char *)src + 1;

179}

180}

181else

182{

183dst = (char *)dst + count - 1;

184src = (char *)src + count - 1;

185while (count--)

186{

187*(char *)dst = *(char *)src;

188dst = (char *)dst - 1;

189src = (char *)src - 1;

190}

191}

192return(ret);

193}

转自： http://www.yqshare.com/string-h-fuction.html