字符串---删除子串（1）

  题目：编写一个函数，删除一个字符串的一部分。函数的原型如下：

int  del_substr(char *str, char const *substr）

      思路：先判断子串是否出现在源字符串中。如果未出现，返回0；如果出现，函数应该把str中位于该子串后面的所有字符复制到该子串的位置，然后函数返回1。如果子串多次出现在源字符串中，函数只删除第一次出现的子串。函数的第二个参数不容许改变。

       在此思路下，很明显，需要额外的一个函数实现找出该子串的位置。

/*
**If the string "substr" apears in "str",delete it.
*/
#include<stdio.h>
#define NULL 0
#define NUL '\0'
#define TRUE 1
#define FALSE 0

/*
** See if the substring begining at 'str' matches the string 'want'. 
**If so,return a pointer to the first character in 'str' after the match.
*/

char *
match(char  *str, char const *want) {
	/*
	**Keep looking while there are more characters in 'want'.
	**We fall out of the loop if we get a match.
	*/
	if (NULL == str || NULL == want)return NULL;
	while (NUL != *want )
		if (*str++ != *want++)
			return NULL;
	return str;
}

int 
del_substr(char *str, char const *substr) {
	char *next =NULL;
	/*
	**Look through the string for the first occurence of the substring.
	*/
	while (NULL != *str) {
		next = match(str, substr);
		if (NULL != next)
			break;
		str++;
	}
	/*
	**If we reached the end of the string,
	**then the substring was not found
	*/
	if (NULL == *str)
		return false;
	/*
	**Delete the substring by copying the bytes after it
	**over the bytes of the substring itself.
	*/

	while (*str++ = *next++)
		;
	return TRUE;
}
int main() {
	char str[] = "I like lie it" ;
	char const* substr = "lie";
	if (del_substr(str, substr)) {
		printf("%s\n", str);
	}
	else
		printf("the substring doesn't apears in str");
	return 0;
}

      本程序来自Kenneth A.Reek所著的《C和指针》，额外添加了main()主函数，所有程序在VS2017下调试通过。