How to Read Specific Data From File in C++
how can I read specific data from file?
I have designed my own method which involves stepping through each character of a text file once and recording the position of all the new lines, but I think someone else might have a more efficient method.
Or.. you can just push the entire text file into a vector (or something similar) and perform searches on the data ye' wish to find.
how can I make program to insert "something2" (without quotes) into something[0] string and "something3" into something[1] string? so my program will get everything after "Something:" and between quotes
#include<iostream> #include<fstream> using namespace std; int main() { fstream infile; int counter = 0; string text_file[10]; infile.open("text.txt"); if(!infile.is_open()) { cout << "\aError! File not found."; cout << "\nFile may have been deleted, moved, or renamed."; cout << "\nPress [ENTER] to continue... "; cin.get(); } while(infile) { infile >> text_file[counter]; counter++; } infile.close(); return 0; } Edited by Clinton Portis because: n/a
well, now I have everything in string, how can I find something in it? I need to check every character anyway :X does anybody knows better method or that one I described?
WaltP 2,905 Posting Sage w/ dash of thyme Team Colleague
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if I recall correctly, the stdio.h library is just an antiquated C version of the modern <iostream> C++ version. it may or may not have file handling properties.. I don't know because I have almost no C experience; however, you should focus on modern coding practices, such as staying away from the old C .h libraries (generally speaking of course)
from what I understand, you wish to read in a line from a text file, and parse it into several useful parts. One method is to read in the text file, 'line at a time' and then split the line up into tokens. This method is useful when your text file may not always strictly adhere to a standard format (random text for example, like a love letter from your girlfriend)
string line; string target; int line_counter = 0; int pos = 0; //ask user what they be lookin' for cout << "Enter something to find within' ye' text file: "; cin >> target; while(infile && pos != string::npos) { //set line counter line_counter++; //read in entire line of text getline(infile, line); //attempt to find what ye' be lookin' for (as in your example, ye' wish to find 'aa') pos = line.find(target); //if found if(pos != string::npos) { cout << target << " found at position " << pos << " in line #" << line_counter << " of the text file. "; } } //if not found if(pos == string::npos) { cout << target << " not found in ye' text file. "; } This method allows ye' to specifically test and identify specific parts of your text file, even if it's all random. The code I provided was based on this example.
Another way to get the parts ye' need out of ye' text file, is to read the entire file 'word at a time'. Using the >> extraction operator, words can be read in one at a time as long as they are 'white space' delimited. This works well for text files that have a standard format, such as the table you have provided because you can assume (for example) that the first word will be (in your case) the line number, second word will always be two letters and a colon, and the last 'word' will always be a number:
string target; int pos = 0; bool is_found = false; //make a custom made container that can hold a line of text struct line_struct { string line_number; string two_letters; string a_number: }; //now make a bunch of containers vector<line_struct> text_file; //make a temporary container line_struct temp; //read the text file while(infile) { //load the temporary container //read in the text file, 'word at a time' infile >> temp.line_number; infile >> temp.two_letters; infile >> temp.a_number; //load the text_file vector with a 'line of text' text_file.push_back(temp); } cout << "Enter something ye' wish to find in ye' text file: "; cin >> target; for(int i=0, size=text_file.size(); i<size; i++) { if(target == text_file[i].line_number || target == text_file[i].two_letters || target == text_file[i].a_number) { pos = i; is_found = true; break; } } // not found if(!is_found) { cout << target << " not found in ye' text file. "; } else //found { cout << target << " found in line " << pos << " of ye' text file. "; } You can neatly package your text file into nice containers and load them easily into a vector because you know your text file follows a specific format. Load the vector and perform user-inquiry based searches as needed.
Edited by Clinton Portis because: n/a
thanks a lot! this helped me greatly, I'm using first example (I changed it a little) and it works nice!
How to Read Specific Data From File in C++
Source: https://www.daniweb.com/programming/software-development/threads/387836/read-specific-data-from-file
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