使用C ++读取文件时省略换行符

Question

I have this code:

#include <iostream>
#include <string>
#include <fstream>

int main()
{
    std::ifstream path("test");
    std::string separator(" ");
    std::string line;
    while (getline(path, line, *separator.c_str())) {
        if (!line.empty() && *line.c_str() != '\n') {
            std::cout << line << std::endl;
        }

        line.clear();
    }

    return 0;
}

The file "test" is populated with numbers, separated by various number of spaces. I need to read only the numbers, one by one and omit spaces and newlines. This code omits the blank spaces but not the newline character.

These are few lines from the input file "test":

     3        19        68        29        29        54        83        53
    14        53       134       124        66        61       133        49
    96       188       243       133        46       -81      -156       -85

I think the problem is that this *line.c_str() != '\\n' is not the proper way to determine if the string line hit newline character and the program keeps printing the newlines!

This one works great:

#include <iostream>
#include <string>
#include <fstream>

int main()
{
    std::ifstream path("test");
    std::string separator(" ");
    std::string line;
    while (getline(path, line, *separator.c_str())) {
        std::string number;
        path >> number;
        std::cout << number << std::endl;
    }

    return 0;
}

Answer 1

使用C ++内置的isdigit函数。

Answer 2

Use the stream operator >> to read integers:

std::ifstream path("test");
int number;
while(path >> number)
    std::cout << number << ", ";
std::cout << "END\n";
return 0;

This will list all the integers in your file, assuming they are separated with space.

The correct usage for getline is getline(path, line) or getline(path, line, ' ') where the last argument can be any character.

*separator.c_str() in this case converts to ' ' . This usage is not recommended.

Likewise *line.c_str() points to the first character in line . To find the last character use

if (line.size())
    cout << line[size()-1] << "\n";

When using getline(path, line) , line will not including the last \\n character.

Here is another example with getline . We read the file line by line, then convert each line to stringstream , and then read the integers from each line:

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>

int main()
{
    std::ifstream path("test");
    std::string line;
    while(getline(path, line))
    {
        std::stringstream ss(line);
        int number;
        while(ss >> number)
            std::cout << number << ", ";
        std::cout << "End of line\n";
    }
    std::cout << "\n";
    return 0;
}