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[英]Why function first-time calling costs much more time than the second time calling it and third and so on?
[英]Why is my read function throwing away the first char when calling it a second time?
我编写了此函数以从cin读取char数组:
#include <iostream>
#include <stdlib.h>
#include <cstring>
#include "main.h"
int read (char* buffer, int size) {
//read from standart input (with whitespaces)
//cin >> buffer;
cin.get(buffer, size);
cin.ignore(1, '\n');
cout << "cin get buffer: " << buffer << endl;
//if not a correct input
if (!cin.good())
return 0;
cout << "cin.good: " << cin.good() << endl;
//user wants to quit
if (!strcmp (buffer, "end"))
return 0;
return 1;
}
当我在我的主returncode = read (first, MAX)
第一次调用此函数时returncode = read (first, MAX)
并输入blabla
,它将“ blabla”读入缓冲区。 (我通过cout-for-loop检查)
当我想读取另一个数组(用于比较),并做完全相同的事情returncode = read(second, MAX)
,它只读取“ labla”,其中second[0]
保持为空。
我的错在哪里 随意询问其余的代码,但我认为错误在于此代码片段内。
先感谢您!
ps:我真的是c ++的新手,所以请耐心:) pps:这是大学考试,我们不允许使用字符串类。
编辑:一个简单的主要来测试以上
main.cpp中:
#include <iostream>
#include "main.h"
#define MAX 200
using namespace std;
int main () {
char first [MAX] = {0};
char second [MAX] = {0};
cout<<"Please enter the first string to compare: "<<endl;
returncode = read (first, MAX);
cout<<"Please enter the second string to compare: "<<endl;
returncode = read (second, MAX);
switch (strcmp_ign_ws(first, second, MAX)) {
case EQUAL:
cout << "Strings are equal!" << endl;
break;
case SMALLER:
cout << "String 1 is lexically smaller!" << endl;
break;
case BIGGER:
cout << "String 1 ist lexically bigger!" << endl;
break;
}
}
和main.h:
#define EQUAL 0
#define SMALLER -1
#define BIGGER 1
int read (char*, int);
int strcmp_ign_ws (char*, char*, int);
int main ();
编辑2:添加字符串比较忽略空白功能
由于错误似乎没有出现在读取功能中,因此这是使用两个输入缓冲区first和second的文件:
#include <stdlib.h>
#include <stdio.h>
#include <cstring>
#include <iostream>
#include <ctype.h>
#include "main.h"
using namespace std;
char * rm_ws (char * buffer, const int size) {
int i,j;
char *output=buffer;
for (i = 0, j = 0; i<size; i++,j++)
{
if (buffer[i]!=' ')
output[j]=buffer[i];
else
j--;
}
output[j]=0;
return output;
}
int strcmp_ign_ws (char * first, char * second, int size) {
first = rm_ws(first, size);
second = rm_ws(second, size);
if (strcmp (first, second) == 0)
return EQUAL;
if (strcmp (first, second) < 0)
return SMALLER;
if (strcmp (first, second) > 0)
return BIGGER;
}
}
ps: rm_ws
函数已经来自stackoverflow
您是在Windows还是基于Unix的系统上称呼它? 在Unix上没有这个问题,所以也许与Windows中结尾的不同行('\\ r \\ n'与'\\ n')有关,并且您使用了
cin.ignore(1, '\n');
不确定是否是问题所在,但只需尝试用简单的方法替换该行
cin.ignore();
经过数小时的调试,我终于得出答案:
在我的rm_ws
函数中有一个小错误:
代替output[j] = 0
它需要在return语句之前output[j-1] = 0
。
谢谢您的帮助!
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