Added space when reading from file in C++ - c++

Question

When I read a string with getline method in C++ it's adding a space in front of my string.
What should I do to eliminate that?
This is my code:
void read_from_file(_Longlong mobile_number) {
string number = to_string(mobile_number);
fstream read(number + "messages_not_seen.txt", ios::in);
_Longlong mobile_numer;
string first_name;
string last_name;
char txt[500];
int Priority;
while (read) {
read >> first_name >> last_name >> mobile_numer;
read.getline(txt, 500);
if (read.eof()) {
break;
}
push(mobile_numer, first_name, last_name, txt);
}
}

Answer 1

The >> operator leaves delimiting whitespace in the stream. Usually, it's not a problem because the >> operator will also ignore leading whitespace, but if you use getline() after the extraction, the space will get included into the string.
You can ignore leading spaces with something like
while (std::isspace(static_cast<unsigned char>(std::cin.peek()))) std::cin.ignore();
Or just call cin.ignore() once if you're sure there is exactly one leading space.
Something you might find helpful is the non-member std::getline() function, which works with std::string instead of character arrays.

Answer 2

If you're using modern C++ (C++-11 and up), you can use lambdas in order to do so.
#include <algorithm>
#include <cctype>
#include <locale>
#include <iostream>
using namespace std; // not recommended, but I assume you're a beginner.
// trim from start (in place)
static inline void ltrim(std::string &s) {
s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](int ch) {
return !std::isspace(ch);
}));
}
void read_from_file(_Longlong mobile_number)
{
string number = to_string(mobile_number);
fstream read(number + "messages_not_seen.txt", ios::in);
_Longlong mobile_numer;
string first_name;
string last_name;
// char txt[500]; // why are you using C-style char here?
string txt; // use string instead
int Priority;
while (read)
{
read >> first_name >> last_name >> mobile_number;
ltrim(read.get(cin, txt));
if (read.eof())
{
break;
}
push(mobile_numer, first_name, last_name, txt);
}
}
And don't forget the main function where you invoke all of these.