C语言 我无法刷新标准输入
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I am not able to flush stdin
提问by Subodh Asthana
How to flush the stdin??
如何刷新标准输入？
Why is it not working in the following code snippet?
为什么它在以下代码片段中不起作用？
#include <string.h>
#include <stdio.h>
#include <malloc.h>
#include <fcntl.h>
int main()
{
int i=0,j=0, sat;
char arg[256];
char * argq;
argq = malloc(sizeof(char)*10);
printf("Input the line\n");
i=read(0, arg, sizeof(char)*9);
arg[i-1]='int c;
while ((c = getchar()) != '\n' && c != EOF);
';
fflush(stdin);
i=read(0, argq, sizeof(char)*5);
argq[i-1]='int c;
while((c = getchar()) != '\n' && c != EOF);
';
puts(arg);
puts(argq);
return 0;
}
Now if i give the input as 11 characters, only 9 should be read but the remaining two characters in the stdin are not flushed and read again in the argq. Why?
现在，如果我将输入设为 11 个字符，则只应读取 9 个字符，但不会刷新 stdin 中的其余两个字符并在 argq 中再次读取。为什么？
Input: 123 456 789
输入：123 456 789
Output: 123 456 89
输出：123 456 89
Why am i getting this 89 as the output?
为什么我得到这个 89 作为输出？
回答by jschmier
I believe fflush is only used with output streams.
我相信 fflush 仅用于输出流。
You might try fpurgeor __fpurgeon Linux. Note that fpurge is nonstandard and not portable. It may not be available to you.
您可以在 Linux 上尝试fpurge或__fpurge。请注意， fpurge 是非标准的且不可移植。您可能无法使用它。
From a Linux fpurge man page: Usually it is a mistake to want to discard input buffers.
来自Linux fpurge 手册页：通常想要丢弃输入缓冲区是错误的。
The most portable solution for flushing stdin would probably be something along the lines of the following:
刷新标准输入最便携的解决方案可能是以下几行：
void readLine(char* input , int nMaxLenIncludingTerminatingNull )
{
fgets(input, nMaxLenIncludingTerminatingNull , stdin);
int nLen = strlen(input);
if ( input[nLen-1] == '\n' )
input[nLen-1] = '##代码##';
}
std::string readLineToStdString(int nMaxLenIncludingTerminatingNull)
{
if ( nMaxLenIncludingTerminatingNull <= 0 )
return "";
char* input = new char[nMaxLenIncludingTerminatingNull];
readLine(input , nMaxLenIncludingTerminatingNull );
string sResult = input;
delete[] input;
input = NULL;
return sResult;
}
回答by jamesdlin
From the comp.lang.c FAQ, see:
从 comp.lang.c 常见问题解答中，请参阅：
回答by jamesdlin
Is how I'd clear the input buffer.
是我清除输入缓冲区的方式。
回答by dirkgently
How to flush the stdin??
如何刷新标准输入？
Flushing input streams is invoking Undefined Behavior. Don't try it.
刷新输入流正在调用未定义的行为。不要尝试。
You can only flush output streams.
您只能刷新输出流。
回答by Nikolai Fetissov
You are overriding the last element of the input in argwith '\0'. That line should be arg[i]='\0';instead (after error and boundary checking you are missing.)
要覆盖在输入的最后一个元素arg用'\0'。那条线应该是arg[i]='\0';（在错误和边界检查之后你丢失了。）
Other's already commented of the flushing part.
其他人已经评论了冲洗部分。
回答by Sunny127
You can't clean stdin in Linux without bumping into scenarios that the command will start waiting for input in some cases. The way to solve it is to replace all std::cin with readLineToStdString():
您无法在 Linux 中清理 stdin，而不会遇到命令在某些情况下开始等待输入的情况。解决方法是将所有 std::cin 替换为 readLineToStdString()：
##代码##This will also allow you to enter spaces in std::cin string.
这也将允许您在 std::cin 字符串中输入空格。
回答by Ng? Thái S?n
In Windows you can use rewind(stdin)fuction.
在 Windows 中，您可以使用rewind(stdin)功能。
