C++ 如何从文件中读取整行（带空格）？
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How to read the whole lines from a file (with spaces)?
提问by Vladimir
I am using STL. I need to read lines from a text file. How to read lines till the first \nbut not till the first ' '(space)?
我正在使用 STL。我需要从文本文件中读取行。如何阅读行直到第一个\n但不读到第一个' '（空格）？
For example, my text file contains:
例如，我的文本文件包含：
Hello world
Hey there
If I write like this:
如果我这样写：
ifstream file("FileWithGreetings.txt");
string str("");
file >> str;
then strwill contain only "Hello" but I need "Hello world" (till the first \n).
thenstr将只包含“Hello”，但我需要“Hello world”（直到第一个\n）。
I thought I could use the method getline()but it demands to specify the number of symbols to be read. In my case, I do not know how many symbols I should read.
我以为我可以使用该方法，getline()但它需要指定要读取的符号数。就我而言，我不知道应该阅读多少个符号。
回答by David Rodríguez - dribeas
You can use getline:
您可以使用 getline：
#include <string>
#include <iostream>
int main() {
std::string line;
if (getline(std::cin,line)) {
// line is the whole line
}
}
回答by user322
using getlinefunction is one option.
or
使用getline函数是一种选择。
或者
getcto read each char with a do-while loop
getc用 do-while 循环读取每个字符
if the file consists of numbers, this would be a better way to read.
如果文件由数字组成，这将是一种更好的阅读方式。
do {
int item=0, pos=0;
c = getc(in);
while((c >= '0') && (c <= '9')) {
item *=10;
item += int(c)-int('0');
c = getc(in);
pos++;
}
if(pos) list.push_back(item);
}while(c != '\n' && !feof(in));
try by modifying this method if your file consists of strings..
如果您的文件由字符串组成，请尝试修改此方法。
回答by user633658
I suggest:
我建议：
#include<fstream>
ifstream reader([filename], [ifstream::in or std::ios_base::in);
if(ifstream){ // confirm stream is in a good state
while(!reader.eof()){
reader.read(std::string, size_t how_long?);
// Then process the std::string as described below
}
}
For the std::string, any variable name will do, and for how long, whatever you feel appropriate or use std::getline as above.
对于 std::string，任何变量名称都可以，并且可以使用多长时间，无论您觉得合适还是使用 std::getline 如上所述。
To process the line, just use an iterator on the std::string:
要处理该行，只需在 std::string 上使用迭代器：
std::string::iterator begin() & std::string::iterator end()
and process the iterator pointer character by character until you have the \n and ' ' you are looking for.
并逐个字符地处理迭代器指针，直到您拥有正在查找的 \n 和 ' '。
回答by Vladimir
Thanks to all of the people who answered me. I made new code for my program, which works:
感谢所有回答我的人。我为我的程序编写了新代码，该代码有效：
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(int argc, char** argv)
{
ifstream ifile(argv[1]);
// ...
while (!ifile.eof())
{
string line("");
if (getline(ifile, line))
{
// the line is a whole line
}
// ...
}
ifile.close();
return 0;
}
