字符串相关函数源代码

/1字符串拷贝函数
char* My_strcpy( char* strDest,const char* strSrc)
{
if(NULL == strDest || NULL == strSrc)
{
return NULL;
}
char* strTemp = strDest;
while( (*strDest++ = *strSrc++) != '\0' );
printf("%s",strDest);
return strTemp;
}


//2字符串长度
int My_strlen(const char* strTest)
{
if ( NULL == strTest)
{
return 0;
}
int i = 0;
while( *strTest++ != '\0' )
i++;
return i;
}


//3查找第一个字符
char* My_strchr(const char* strTest,int c)
{
if ( NULL == strTest)
{
return NULL;
}
//char* strTemp = strTest;
while( *strTest++ != c)
if (*strTest)
{
return (char*)strTest;
}
return NULL;
}


//4字符串比较函数
int My_strcmp(const char* str1,const char* str2)
{
if ( NULL == str1 || NULL == str2)
{
return -10;
}
while( *str1 && *str2 && (*str1 == *str2) )
{
str1++;
str2++;
}
return(*str1 - *str2);
}


//5字符串连接函数
char* My_strcat( char *strDestination, const char *strSource)
{
if ( NULL == strDestination || NULL == strSource)
{
return NULL;
}
char* strTemp = strDestination;
while( *strDestination != '\0')
{
strDestination++;
}
while( ((*strDestination++ = *strSource++)) != '\0' );
return strTemp;
}


//6字符串拷贝到新的内存
char* My_strdup(const char* strDestination)
{
if ( NULL == strDestination)
{
return NULL;
}
int nLength = 0;
char* strTest = (char*)strDestination;
while( *strTest++ != '\0')
{
nLength++;
}
char* strTemp = (char*)malloc(nLength+1);
char* strReturn = strTemp;
while( (*strTemp = *strDestination) != '\0')
{
strTemp++;
strDestination++;
}
return strReturn;
}


//7查找字符串
char* My_strstr(const char* strSrc,const char* str)
{
//assert(strSrc != NULL && str != NULL);
const char *s = strSrc;
const char *t = str;
for (; *t != '\0'; ++ strSrc)
{
printf("%s\n",strSrc);
for (s = strSrc, t = str; *t != '\0' && *s == *t; ++s, ++t)
NULL;
if (*t == '\0')
return (char *) strSrc;
}
return NULL;

1. }