对于短输入有效，对于长输入失败。如何解决？
我有这个程序可以在字符串中查找子字符串。它适用于小输入。但对于长输入会失败。这是程序：
//Find Substring in given String
#include <stdio.h>
#include <string.h>
main()
{
//Variable Initialization
int i=0,j=0,k=0;
char sentence[50],temp[50],search[50];
//Gets Strings
printf("Enter Sentence: ");
fgets(sentence,50,stdin);
printf("Enter Search: ");
fgets(search,50,stdin);
//Actual Work Loop
while(sentence[i]!='\0')
{
k=i;j=0;
while(sentence[k]==search[j])
{
temp[j]=sentence[k];
j++;
k++;
}
if(strcmp(temp,search)==0)
break;
i++;
}
//Output Printing
printf("Found string at: %d \n",k-strlen(search));
}
适用于：
Enter Sentence: good evening
Enter Search: evening
Found string at 6
失败于：
Enter Sentence: dear god please make this work
Enter Search: make
Found string at 25
这是完全错误的。有哪位高手可以帮我找到解决办法吗？
PS： 这有点像重新发明轮子，因为 strstr() 具有此功能。但我正在尝试一种非图书馆的方式来做到这一点。
I've this program which finds substring in a string. It works for small inputs. But fails for long inputs. Here's the program:
//Find Substring in given String
#include <stdio.h>
#include <string.h>
main()
{
//Variable Initialization
int i=0,j=0,k=0;
char sentence[50],temp[50],search[50];
//Gets Strings
printf("Enter Sentence: ");
fgets(sentence,50,stdin);
printf("Enter Search: ");
fgets(search,50,stdin);
//Actual Work Loop
while(sentence[i]!='\0')
{
k=i;j=0;
while(sentence[k]==search[j])
{
temp[j]=sentence[k];
j++;
k++;
}
if(strcmp(temp,search)==0)
break;
i++;
}
//Output Printing
printf("Found string at: %d \n",k-strlen(search));
}
Works for:
Enter Sentence: good evening
Enter Search: evening
Found string at 6
Fails for:
Enter Sentence: dear god please make this work
Enter Search: make
Found string at 25
Which is totally wrong. Can any expert find me a solution?
P.S: This is kinda like reinventing the wheel since strstr() has this functionality. But I'm trying for a non-library way of doing it.
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评论（3）
您需要使用
strncmp而不是strcmp并将比较长度设置为等于strlen(search)。或者您可以使用'\0'终止 temp。You need to use
strncmprather thanstrcmpand set the comparison length equal tostrlen(search). Either that or you could just terminate temp with a'\0'.好吧，首先，在第二种情况下“temp”不会以空终止。这就是为什么你的第一个案例有效；如果你搜索“好”，它就不起作用。
Well, to start with, "temp" won't be null terminated in the second case. That's why your first case works; it wouldn't work if you'd searched for "good."
如果您想完全避免 strcmp，那么您已经完成了 99% 的工作。只需在退出比较循环时根据您的标记/搜索字符串长度检查 j ，您就会知道是否有匹配项。
If you wanted to avoid the strcmp completely, you are already doing 99% of its work. Just check j against your token/search string length upon exit of your compare loop and you'll know if you have a match.