bs

#include <iostream>
#include <cmath>
#include <stdlib.h>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;
string removeSpaces(string s);
int main()
{
    fstream fin("text1.txt", ios::in | ios::out);
    //string a;
    if (!fin)
    {
        cout << "Can't open file" << endl;
    }
    stringstream strs;
    strs << fin.rdbuf();
    fin.seekp(0);
    string line;
    while (getline(strs, line))
    {
        if (!line.empty())
        {
            line = removeSpaces(line);
            fin << line << std::endl;
        }
    }
    fin.close();
    system("pause");
    return 0;
}
string removeSpaces(string s)
{
    for (int j = 0; j < s.length(); j++)
    {
        if (s[j] == ' ')
        {
            while (s[j + 1] == ' ') s.erase(j + 1, 1);
        }
    }
    return s;
}