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I have a problem because this is my first time encountering some functions from C that I need to convert into C++.
Code:
FILE *pokf;
char name[10],gender;
int age, i, n, b1=0, b2=0;
float p;
pokf=fopen("Data.txt","r");
while (feof(pokf)==0) {
fscanf (pokf,"%s %c %d %f", &name, &gender, &age, &p);
if (gender=='Z') b1++;
if (p>=4.50 ) b2++; }
fclose(pokf);
I can write:
ifstream input;
input.open("Data.txt");
But then I don't know what to use instead of pokf because I can't use FILE *pokf anymore.
What to use instead of functions feof and fscanf?
The rough equivalent of fscanf is operator>> and I wouldn't worry about feof since it's being used incorrectly. So
while (feof(pokf)==0) {
fscanf (pokf,"%s %c %d %f", &name, &gender, &age, &p);
...
becomes
while (pokf >> name >> gender >> age >> p) {
...
Although using char name[10] in C++ will work, it has the obvious problem that you are limited to names of 9 characters of less. In C++ you should use std::string instead of a char array.
You should be able to use FILE *pokf in c++, here is an example http://www.cplusplus.com/reference/cstdio/feof/ where you can see how to open files in c++
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main () {
string line;
ifstream myfile ("example.txt");
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
cout << line << '\n';
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
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I have been asked to develop program to count no. of lines and words in the file, this is my trial, my teacher said that I cant use >> operator for counting words and comparing but I could not handle it.
#include <iostream>
#include <fstream>
using namespace std;
int numberLines = 0;
int numberWords = 0;
void numberOfLines(){
cout<<"number of lines is " << numberLines << endl;
}
void numberWords(){
cout << "number of words is " << numberWords <<endl;
}
int main(){
string line;
char a = '';
ifstream myfile("files.txt");
if(myfile.is_open()){
while(!myfile.eof()){
getline(myfile,line);
cout<< line << endl;
numberLines++;
}
if ( a == ' '){
NumberWords++;
}
}
myfile.close();
}
numberOfLines();
numberOfWords ();
}
What you can do is add a 3rd argument to getline(). This lets it pull data from the stream until it hits a character. Doing getline(cin, line, ' ')takes all the data until the next and puts it into line. Your code might look like:
while(getline(inFile, line))
{
++numlines;
stringstream lineStream(line);
while(getline(lineStream, line, ' '))
{
++numWords;
}
}
The outer loop goes through the file and stores each line into line, then the inner goes through that line and counts each space. which correlates to a word.
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it is file
it is class
class size
loving file
becomes
loving file
class size
it is class
it is file
simple by primitive data type never use vector , string etc . simple file handling in cpp
As you would not like to use arrays, vectors or anything like that here you are a solution that may help you.
Note: using a temp storage will make it more compact.
The idea is to use three function:
1- get_line_num: counts line numbers of the file.
2- goto_line: puts the reading cursor into a specific line.
3- reset: put the reading cursor in the beginning of the file.
Program has a lot of I/O which is not good, but as you do not want to use advanced structures, this may help.
algorithm:
open original file.
open temp file.
loop from last line to first line
read line from input file.
add the line into the temp output file
end loop.
delete the old original file.
rename the temp file same as the original file.
Headers:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int get_line_num(ifstream& myfile);
ifstream& goto_line(ifstream& myfile, int line_num);
void reset(ifstream& myfile);
int main()
{
ifstream in;
ofstream out;
string line;
char* original = "original file name";
char* dest = "temp file name";
in.open(original);
out.open(dest, ios::app);
int num_of_lines = get_line_num(in);
for (int i = num_of_lines ; i ; --i)
{
goto_line(in, i);
getline(in, line);
reset (in);
out << line << "\n";
}
in.close();
out.close();
remove(original);
rename(dest, original);
cout <<"\n\n\n";
}
int get_line_num(ifstream& myfile)
{
int number_of_lines = 0;
string line;
while (getline(myfile, line))
++number_of_lines;
reset (myfile);
return number_of_lines;
}
ifstream& goto_line(ifstream& myfile, int line_num)
{
string s;
myfile.seekg(ios::beg);
for(int i = 1; i < line_num; ++i)
getline(myfile, s);
return myfile;
}
void reset(ifstream& myfile)
{
myfile.clear();
myfile.seekg(0, ios::beg);
}
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i want to convert a sentence like 'good boy' to ascii code . i know the code that is a loop and print the ascii code of each character of sentence but i don't want this. i want that the ascii code of sentence (all characters alltogether) in long for example 1259788712..
You can use string to handle it.
#include <iostream>
#include <sstream> // use stringstream
using namespace std;
// turn int into string
string IntTOstring(int);
int main(void)
{
string sIn,sOut;
// input
sIn = "good boy";
sOut="";
for (int i=0 ; i<sIn.length() ; i++ ) {
// get one char from sIn each time
int temp=sIn.c_str()[i];
// turn int into string & save in sOut
sOut += IntTOstring(temp);
}
cout << sOut << endl;
return 0;
}
// use stringstream to convert int to string
string IntTOstring(int i){
stringstream ss;
ss << i;
return ss.str();
}
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I need to read from file line by line and print it on the screen:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
ofstream out("note.txt");
for (int i = 0; i < 10; i++)
out << i << " " << (i<<1) << "\n";
out.close();
ifstream fin;
fin.open("note.txt");
string line;
for (int i = 0; i < 10; ++i)
{
getline(fin, line);
cout << line << "\n";
}
return 0;
}
Is this approach correct? Cant I do it without a string variable (without string line in code)?
Instead of using a for loop you can use a while loop:
#include<iostream>
#include<string>
#include<fstream>
using namespace std;
int main() {
string line;
ifstream out("note.txt");
while(getline(out, line)) {
cout << line << endl;
}
out.close();
}
If you are forced not to use strings then you can try a char buffer char buf[1024]. It must be pointed out that this approach is dangerous and error prone. If a line has more than 1024 characters then a buffer overflow will occur. Buffer overflow is the cause of many vulnerabilities and crashes. That being said, if you really have to use this method I would suggest you to be very careful by making the appropriate checks.
Copying a file verbatim is a simple as streaming out its stream buffer:
ifstream fin;
fin.open("note.txt");
std::cout << fin.rdbuf();
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Say I have a text file containing 10 lines. I want to move to line #5, clear everything below it, and append some new texts after that. What is the most compact way to achieve this using C++ of stream (just in case I missed some ofstream features)?
Read N lines while writing to a second file, then write all the new text to the new file after that.
Use IOstream to open the file and store the first five lines in an array and recreate the test file using the array and whatever other lines you want. Here is a code example:
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main () {
const int linesToRead = 5; //How many lines to read before stopping
string lines [linesToRead];
int line = 0;
ifstream myinputfile ("example.txt");
if (myinputfile.is_open())
{
while ( myinputfile.good() && line<=linesToRead )
{
if(line<linesToRead)
{ //Stop reading at line 5
getline (myinputfile,lines[line]);
cout << lines[line];
}
line++;
}
myinputfile.close();
}
else cout << "Unable to open file";
//Begin creating new file
const int numberOfNewLines = 7;
string newlines[numberOfNewLines] = {"These", "are", "some", "of", "the", "new", "lines"}; //lines to be added after the previous 5
ofstream myoutputfile ("example.txt");
if (myoutputfile.is_open())
{
for(int i = 0; i<linesToRead; i++){
myoutputfile << lines[i] << "\n";
}
for(int i = 0; i<numberOfNewLines; i++){
myoutputfile << newlines[i] << "\n";
}
myoutputfile.close();
}
else cout << "Unable to open file";
return 0;
}