1.实现基本的c语言库函数：
int myStrlen( const char* str);//根据传入的字符串首地址获取字符串长度；返回值为长度
int myStrlen(const char* str)
{
if (str == NULL)
return 0;
int length=0;
while (*str != ‘\0‘)
{
length++;
str++;
}
return length;
}
void* myStrcpy(char* des, const char* source);//复制source到des
void* myStrcpy(char* des, const char* source)
{
if (des == NULL || source == NULL)
return NULL;
char *desbak = des;
while (((*des++) = (*source++)) != ‘\0‘);
*des = ‘\0‘;
return desbak;
}
void * myStrcat(char* des, const char *source);//将source添加到des的末尾
void * myStrcat(char* des, const char *source)
{
if (source == NULL || des == NULL)
return NULL;
if (myStrlen(source) == 0)
return des;
des = (char*)realloc(des, myStrlen(des) + myStrlen(source) + 1);
int i = myStrlen(des);
while (*source != ‘\0‘)
{
*(des + i) = *source;
i++;
source++;
}
*(des + i) = ‘\0‘;
return des;
}
char* myStrrev(const char* str); //字符串逆转
char* myStrrev(const char* str)
{
int i = 0;
int len = myStrlen(str);
char* res = (char*)calloc(len+1,sizeof(char));
*(res + len) = ‘\0‘;
for (i = len - 1; i >= 0; i--,str++)
{
*(res + i) = *str;
}
return res;
}
int str2int(const char* str);//将整数字符串转化为整数;返回值为结果整数,失败返回-1
int str2int(const char* str)
{
if (str == NULL)
return -1;
char* strbak = str;
int res = 0;
while (*str != ‘\0‘)
{
if (*str<‘0‘ || *str>‘9‘)
{
return -1;
}
str++;
}
str = strbak;
while (*str != ‘\0‘)
{
res *= 10;
int temp = *str - 48;
res += temp;
str++;
}
return res;
}
char* int2str(int num);//将正整数转化为字符串，返回字符串首地址
char* int2str(unsigned int num)
{
int numbak = num;
int n=0;//计算int位数
while (num != 0)
{
n++;
num /= 10;
}
char* res = (char*)calloc(n+1,sizeof(char));
char* resbak=res;
num = numbak;
while (num != 0)
{
*res = num % 10 + 48;
res++;
num /= 10;
}
*res = ‘\0‘;
resbak = myStrrev(resbak);
return resbak;
}
2.根据上面编写的库函数，实现一些扩展的功能：
typedef struct _myString //定义字符串结构体，包括字符串及其长度
{
char *p;
int length;
} myString;
int initString(myString *string, char* str);//初始化字符串
int initString(myString *string, char* str)
{
if (str == NULL)
return -1;
int length = myStrlen(str);
string->p = (char*)calloc(length + 1,sizeof(char));
myStrcpy(string->p,str);
string->length = length;
return 1;
}
void * findChar(const myString *string, const char findCh);//找到特定的字符,返回首地址
void * findChar(const myString *string, char findCh)
{
char* s = string->p;
while (*s != ‘\0‘)
{
if (*s== findCh)
return s;
s++;
}
return NULL;
}
void * findString(const myString *string,const char* findStr);//找到字符串，返回首地址，找不到返回null
void * findString(const myString *string,const char* findStr)
{
if (NULL == findStr)
return NULL;
if (myStrlen(findStr) > myStrlen(string->p))
return NULL;
char* s = string->p;
char*sp = NULL;
int i = 0,j=0;
for (i = 0; i < string->length - 1; i++)
{
char* fs = findStr;
if (*(s + i) == *(fs))
{
sp = s + i;
for (j = 0; j < myStrlen(findStr) - 1; j++)
{
sp++;
fs++;
if (*sp != *fs)
break;
}
if (j ==myStrlen(findStr) - 1)
return s + i;
}
}
return NULL;
}
int addChar(myString *string, char addCh, char* pos);//pos为null则在string的后面添加，否则在指定位置添加一个字符；返回-1表示操作失败
int addChar(myString *string, char addCh, char* pos)//pos为NULL表示在字符串后面添加
{
if (pos == NULL)
{
//string->p = (char *)realloc(string->p, string->length + 2);
myStrcat(string->p, &addCh);
string->length += 1;
return 1;
}
if (pos<string->p || pos>string->p + string->length)
return -1;
int i = string->length , addLength = pos-string->p ;
string->p = (char *)realloc(string->p,string->length+2);
char *s = string->p;
*(s + i +1) = ‘\0‘;
for (i = string->length ; i > addLength; i--)
{
*(s + i) = *(s+i-1);
}
*(s + i) = addCh;
string->length += 1;
return 1;
}
int addString(myString *string, const char* addStr, char* pos);//pos为null则在string的后面添加，否则在指定位置添加一个字符串；返回-1表示操作失败
int addString(myString *string, const char* addStr, char* pos)
{
if (pos == NULL)
{
myStrcat(string->p, addStr);
string->length += myStrlen(addStr);
return 1;
}
if (pos<string->p || pos>string->p + string->length||addStr==NULL)
return -1;
string->length += myStrlen(addStr);
int i = string->length+myStrlen(addStr), addLength = pos - string->p;
string->p = (char *)realloc(string->p, string->length +myStrlen(addStr)+1 );
char *s = string->p;
*(s + i ) = ‘\0‘;
for (i = string->length+myStrlen(addStr)-1; i > addLength; i--)
{
*(s + i) = *(s + i - myStrlen(addStr));
}
while (*addStr != ‘\0‘)
{
*(s + i) = *addStr;
i++;
addStr++;
}
return 1;
}
void deleteChar(myString *string,char deleteCh,int tag);//tag为1，则删除所有的指定字符；否则，只删除第一个
void deleteChar(myString *string, char deleteCh,int tag)
{
char * pos = (char*)findChar(string, deleteCh);
if (pos == NULL)
return ;
while (*pos != ‘\0‘)
{
*pos = *(pos+ 1);
pos++;
}
string->length -= 1;
if (tag == 1)
{
while (findChar(string, deleteCh) != NULL)
deleteChar(string, deleteCh,1);
}
}
void deleteString(myString *string,const char *deleteStr,int tag);//tag为1，则删除所有的指定字符；否则，只删除第一个；
void deleteString(myString *string, const char *deleteStr,int tag)
{
char * pos = (char*)findString(string, deleteStr);
if (pos == NULL)
return;
while (*(pos+myStrlen(deleteStr)-1) != ‘\0‘)
{
*pos = *(pos + myStrlen(deleteStr));
pos++;
}
string->length -= myStrlen(deleteStr);
if (tag ==1)
{
while (findString(string, deleteStr) != NULL)
deleteString(string, deleteStr,1);
}
}
void updateChar(myString *string,char oldCh,char newCh);//更新一个字符
void updateChar(myString *string, char oldCh, char newCh)
{
char* pos;
if ((pos = findChar(string, oldCh)) == NULL)
return;
*pos = newCh;
while (findChar(string, oldCh) != NULL)
updateChar(string,oldCh,newCh);
}
void updateString(myString *string, char* oldStr, const char* newStr);//更新字符串
void updateString(myString *string, char* oldStr, const char* newStr)
{
if (newStr == NULL)
return;
char* pos;
if ((pos = findString(string, oldStr)) == NULL)
return;
deleteString(string,oldStr,0);
addString(string,newStr,pos);
while (findString(string, oldStr) != NULL)
{
updateString(string,oldStr,newStr);
}
}
原文：http://www.cnblogs.com/HIT-LYT/p/4280906.html