C++ Read in a file like a grid - c++

Question

I'm coding in C++ and I'm trying to read in a file that I'd like to access certain chars at later. As in, what is the char at (line x, char y), at any given point in the file.
My only thought right now is to look for a newline character, and somehow index them so that I can refer back to newline x, check the length of a line, and pull a char at whatever position given the line length.
I'm not sure if that is a good approach or not.

Answer 1

Try this (for character in line "lineNum" and column "columnNum"):
ifstream inf;
inf.open(filename); //filename being c-string
string str;
for (int i = 0; i < lineNum; i++)
{
std::getline(inf, str);
}
This way "str" stores the line you are interested in (automatically checks for newline character and stops).
Then you can use:
char chr = str[columnNum];
to store the character you want in "chr" variable. And don't forget:
inf.close();
Unfortunately, to my knowledge you need to repeat this process every time you want to access a character.

Answer 2

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>
#define FILENAME "File.txt"
class FileGrid {
public:
typedef std::vector<std::string> Line;
typedef std::vector<std::string>::const_iterator LineIter;
typedef std::vector<std::vector<std::string>> StringMap;
typedef std::vector<std::vector<std::string>>::const_iterator StringMapIter;
void FillGrid(char* fileName) {
grid.clear();
std::ifstream in(FILENAME, std::ifstream::in);
if (!in.is_open()) {
std::cout << "problem reading " << FILENAME << std::endl;
return;
}
std::string words;
std::string word;
std::stringbuf buffer;
while (in.is_open() && std::getline(in, words)) {
std::stringstream ss(words);
Line line;
while (ss >> word) {
line.push_back(word);
}
grid.push_back(line);
}
}
void PrintGrid() {
StringMapIter b = grid.begin();
StringMapIter e = grid.end();
std::cout << "\t\tFile Content:" << std::endl;
while(b != e) {
for (unsigned int i = 0; i < b->size(); ++i) {
std::cout << b->operator[](i) << " ";
}
std::cout << std::endl;
++b;
}
}
char const & GetChar(int lineNo, int charNo) {
// LineNo checks etc
Line const & line = grid[lineNo];
for(std::string const & word : line ) {
if(charNo > word.size() + 1) {
charNo -= word.size() + 1;
}
else {
return word[charNo];
}
}
throw std::exception("charNo higher");
}
private:
StringMap grid;
};
void main() {
FileGrid grid;
grid.FillGrid(FILENAME);
grid.PrintGrid();
std::cout << grid.GetChar(0, 3); // should return first line, 4th character
}
Not the best code I've ever written but pretty much what I could do in a short time.
FileGrid handles reading and accessing the data. It reads the file line by line and stores it in a std::vector. When it finishes reading a line, it pushes that into another std::vector. In the end, we have a (sort of) 2D array of strings.
Again, not the best code and definitely not the most optimized code but the idea is still the same: read from the file line by line, separate each word and put them into an array of strings. If you can't use STL, you can dynamically create a 2D array for each line but since I don't know the specific requirements of your question, I just wrote something simple and bruteforce to show you the main way of storing grid of strings into the memory.

Answer 3

As long as it works. But reading the entire file into memory, if that's an option, would be simpler.