Member Avatar for Carrots

Hi there,

I am trying to read values from a .txt file using stringstreams and plan to enter the values into a map,

I am reading into a buffer, but it contains spaces and I believe a character which represent the end of line.

Here is my program so far:

#include <map>
#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;

int main()
{
	//I eventually plan to enter the values into a map
	map<string, string> mapname;

	//Ask for the filename to open
	char fileName[20];
	cout << "Enter the name of the .txt file that you would like to open (eg: file.txt) : " << endl;
	cin >> fileName;

	//create the fstream
	ifstream in(fileName);

	//create a stringstream object called buffer
	stringstream buffer;

	//read the file into the buffer
	buffer << in.rdbuf();

	//Now I want to split the buffer so it can be entered into a map, like a phone book

	//close the connection to the .txt file 
	in.close();

	system ("pause");
	return 0;
}

Here is an example of file.txt:

A1 John Doe
A2 John Smith

So I'm trying to put 'A2' into the key part of the map, and 'John Doe' into the mapped part of the map.

I'm trying to do it as simply as possible, just using the standard library.

Really appreciate any advice with this.

Thanks a lot :)

  • 3 Contributors
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  • 6 Hours Discussion Span
  • Latest Post Latest Post by Narue

Dani AI

Generated

— for input lines like A1 John Doe, a clear, robust pattern is to read the file line-by-line, split at the first whitespace, trim any leftover carriage-return/whitespace, then insert the pair into the map. This follows the spirit of 's temporary-string idea and complements 's stream-based extraction while adding handling for Windows CRLF and duplicate-key decisions.

#include <fstream>
#include <string>
#include <map>

// trim in-place (spaces, tabs, CR, LF)
static inline void trim(std::string &s) {
    const char* ws = " \t\n\r";
    auto b = s.find_first_not_of(ws);
    if (b == std::string::npos) { s.clear(); return; }
    auto e = s.find_last_not_of(ws);
    s = s.substr(b, e - b + 1);
}

int main() {
    std::ifstream in("file.txt");
    std::map<std::string, std::string> phonebook;
    std::string line;
    while (std::getline(in, line)) {
        if (!line.empty() && line.back() == '\r') line.pop_back(); // strip CR from Windows files
        auto sep = line.find_first_of(" \t");
        if (sep == std::string::npos) continue; // skip malformed/empty lines
        std::string key = line.substr(0, sep);
        std::string value = line.substr(sep + 1);
        trim(key); trim(value);
        phonebook.emplace(key, value); // emplace avoids overwriting existing keys
    }
}

Notes and troubleshooting: a trailing \r (CR) is a common source of odd characters when the file came from Windows — the line.pop_back() guard removes that. Use emplace and check its return if overwriting must be detected; choose std::multimap or map<string, vector<string>> if duplicate keys are expected. Prefer std::string for filenames and let RAII close the ifstream. If keys themselves may contain spaces or have a different delimiter, adjust the split logic (for example, parse a quoted key or use a fixed delimiter).

Recommended Answers

All 2 Replies

Member Avatar for Topi Ojala

I would take the data from stringstream to a temporary string, maybe 2 temporary strings. After that I could make_pairs out of them and insert them into the map.

Not sure if that is the best option, and in that case the stringstream would not even be necessary. There might be some useful stringstream operators used in parsing the data.

Member Avatar for Narue

A stringstream is still a stream. Just do it the same way you would with cin:

string key, value;

while ( buffer>> key && getline ( buffer, value ) )
  mapname[key] = value;
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