C++ cin char 逐个符号读取
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C++ cin char read symbol-by-symbol
提问by tucnak
I need to read symbol-by-symbol. But I don't know how to read until end of input. As exemple test system will cin>>somecharvariable m times. I have to read symbol-by-symbol all characters. Only m times. How I can do it?
我需要逐个符号阅读。但我不知道如何阅读，直到输入结束。例如，测试系统将 cin>>somecharvariable m 次。我必须逐个符号阅读所有字符。只有m次。我该怎么做？
采纳答案by Kerrek SB
If you want formatted input character-by-character, do this:
如果要逐字符格式化输入，请执行以下操作：
char c;
while (infile >> c)
{
// process character c
}
If you want to read raw bytes, do this:
如果要读取原始字节，请执行以下操作：
char b;
while (infile.get(b))
// while(infile.read(&b, 1) // alternative, compare and profile
{
// process byte b
}
In either case, infileshould be of type std::istream &or similar, such as a file or std::cin.
在任何一种情况下，infile都应该是类型std::istream &或类似的，例如文件或std::cin.
回答by Konrad Rudolph
There are several ways to read one character at a time until you have read them all, and none of them is necessarily the best.
有多种方法可以一次阅读一个字符，直到您全部阅读完为止，而且没有一种方法一定是最好的。
Personally, I'd go with the following code:
就个人而言，我会使用以下代码：
char c;
while (cin.get(c)) {
// Process c here.
}
If you only need to read mcharacters, consider using a forloop:
如果您只需要读取m字符，请考虑使用for循环：
char c;
for (unsigned int i = 0; i < m && cin.get(c); ++i) {
// Process c here.
}
This runs the loop as long as two conditions are fulfilled: (1) less than mcharacters have been read, and (2) there are still characters to read.
只要满足两个条件，就会运行循环：(1)m已读取的字符数少于，以及 (2) 仍有要读取的字符。
However, both solutions have a drawback: they are relatively inefficient. It's more efficient to read the mcharacters in one go.
然而，这两种解决方案都有一个缺点：它们的效率相对较低。一口气读完m字符效率更高。
So first allocate a big enough buffer to store mchars and then attempt to read them:
所以首先分配一个足够大的缓冲区来存储m字符，然后尝试读取它们：
std::vector<char> buffer(m);
cin.read(&m[0], m);
unsigned total_read = cin.gcount();
Notice the last line – this will tell you whether mcharacters have been actually read.
注意最后一行——这将告诉您m字符是否已被实际读取。
回答by Sergey
Try this:
尝试这个：
#include <iostream>
using std::cin;
using std::cout;
int main(int argc, char *argv[])
{
char ch;
unsigned m = 10;
while (cin && m--) {
cin.read(&ch, sizeof(ch));
cout << ch;
}
return 0;
}
