So I am not sure how to get the output to like a .txt file, the code keeps giving me a .txt file but it is always empty. I know I am supposed to include a line where it outputs the information but I am uncertain of what to put in the line since its a void function and it doesn't return anything, would changing it to a different type of function solve the problem?
Code:
#include <iostream>
#include <string>
#include <fstream>
#include "ArgumentManager.h"
using namespace std;
void permute(string a, int l, int r)
{
if (l == r)
cout<<a<<endl;
else
{
for (int i = l; i <= r; i++)
{
swap(a[l], a[i]);
permute(a, l+1, r);
swap(a[l], a[i]);
}
}
}
int main(int argc, char* argv[])
{
ArgumentManager am(argc, argv);
ifstream input;
ofstream output;
string infileName = am.get("input");
string outfileName = am.get("output");
input.open(infileName);
output.open(outfileName);
string str;
int n = str.size();
permute(str, 0, n-1);
return 0;
}
I havent worked with ArgumentManager before in C++.
But can you use something like:
// basic file operations
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}
I think instead of passing the output to cout, you should pass it to myfile object.
Related
I am reading a file using fstream and getline functions. I want to give a starting position e.g. my file has 13 lines I want to start reading it from 7th line for example. Here is my code:
#include<iostream>
#include <stdlib.h>
#include <string>
#include <vector>
#include<iterator> // for iterators
#include<map>
using namespace std;
int main()
{
string line;
int start= 7;
unsigned long int index;
For( int z=1; z<=13; z++){
if (f_node.is_open())
{
getline(f_node, line);
if ((line.find("$EndNodes") != string::npos))
{
cout << "$EndNodes found file closed .... " << endl;
f_node.close();
return false;
}
// Point index.
int i = 0;
int j = line.find_first_of(" ", i);
index = strtoul((line.substr(i, j)).c_str(), NULL, 0);//
}
}
I am reading only indexes and I want to start it from 7th index How to do it?
To discard some number of lines, something like:
#include <fstream>
#include <string>
int main() {
std::ifstream infile{"myfile.txt"};
std::string line;
int starting_line = 7;
// Read and discard beginning lines
for (int n = 1; n < starting_line; n += 1) {
if (!std::getline(infile, line)) {
// Error or premature end of file! Handle appropriately.
}
}
while (std::getline(infile, line)) {
// Do something with the lines you care about.
}
return 0;
}
Except with actual error checking and handling and such.
"there is no way to tell code the starting position like seekg and tellg?" No. NL is just like any other character, it does not receive any special treatment.
You simply must scan the stream, counting the new-line character:
std::istream& seek_line(std::istream& is, const int n, std::ios_base::seekdir way = std::ios_base::beg)
{
is.seekg(0, way);
int i = 0;
char c;
while (is.get(c) && i < n)
if (c == '\n')
++i;
is.putback(c);
return is;
}
And this is how you use the above function:
int main()
{
using namespace std;
ifstream is{ "c:\\temp\\test.txt" };
if (!is)
return -1;
if (!seek_line(is, 3))
return -2;
string s;
getline(is, s);
cout << s << endl;
return 0;
}
I am having what seems to be a common issue however reading through the replies to the similar questions I can't find the solution to my issue at all as I have already done what they are suggesting such as making the variable an array. I have the following code:
#include "stdafx.h"
#include <cstring>
#include <fstream>
#include <iostream>
#include <string>
#include <algorithm>
#include <future>
using namespace std;
string eng2Str[4] = { "money", "politics", "RT", "#"};
int resArr[4];
int main()
{
engine2(eng2Str[4], resArr[4]);
system("Pause");
system("cls");
return 0;
}
void engine2(string &eng2Str, int &resArr)
{
ifstream fin;
fin.open("sampleTweets.csv");
int fcount = 0;
string line;
for (int i = 0; i < 4; i++) {
while (getline(fin, line)) {
if (line.find(eng2Str[i]) != string::npos) {
++fcount;
}
}
resArr[i] = fcount;
}
fin.close();
return;
}
Before you mark as duplicate I have made sure of the following:
The array and variable I am trying to assign are both int
Its an array
The error is:
expression must have pointer-to-object type
The error is occurring at the "resArr[i] = fcount;" line and am not sure why as resArr is an int array and I am trying to assign it a value from another int variable. I am quite new to C++ so any help would be great as I am really stuck!
Thanks!
The problem is that you've declared your function to take a reference to a single string and int, not arrays. It should be:
void engine2(string *eng2Str, int *resArr)
or:
void engine2(string eng2Str[], int resArr[])
Then when you call it, you can give the array names as arguments:
engine2(eng2Str, resArr);
Another problem is the while loop in the function. This will read the entire file during the first iteration of the for() loop. Other iterations will not have anything to read, since it will be at the end of the file already. You could seek back to the beginning of the file, but a better way would be to rearrange the two loops so you just need to read the file once.
while (getline(fin, line)) {
for (int i = 0; i < 4; i++) {
if (line.find(eng2Str[i]) != string::npos) {
resArr[i]++;
}
}
}
I would suggest to use std::vector instead of pure C array.
In your code, there are more issues.
You are passing the fourth element of both arrays to the engine2 function.
From your definition of void engine2(string &eng2Str, int &resArr) you expect reference to a string (not array / vector) and an address / reference of int - you need to pass an pointer to the first element of resArr.
#include <cstring>
#include <fstream>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <future>
using namespace std;
vector<string> eng2Str = { "money", "politics", "RT", "#" };
int resArr[4] = {};
void engine2(const vector<string>& eng2Str, int* resArr)
{
ifstream fin;
fin.open("sampleTweets.csv");
int fcount = 0;
string line;
for (int i = 0; i < 4; i++)
{
while (getline(fin, line))
{
if (line.find(eng2Str[i]) != string::npos)
{
++fcount;
}
}
resArr[i] = fcount;
}
fin.close();
return;
}
int main()
{
engine2(eng2Str, resArr);
system("Pause");
system("cls");
return 0;
}
I am still a newbie in programming. I am writing a program of 2D Snell's Law. I know the problem may due to wrong localisations in Xcode, but I am writing in C++ only and g++ even gives me segmentation fault error after compiling successfully.
Here are my code for main function:
#include <string>
#include "Snell.hpp"
int main(int argc, const char * argv[]){//thread 1 exc_bad_access (code=2 address=0x7fff5f238304)
string filename;
double time;
Snell S[3600];
for (int i=1; i<=1; i++) {
while (S[i].angle_tr>0) {
filename="VPVSMOD"+to_string(i)+".txt";
S[i].Open(filename);
time=S[i].Locate(i);
cout<<"The "<<i<<"th event takes "<<time<<" seconds to reach the destination"<<endl;
S[i].angle_tr-=0.01;
}
}
return 0;
}
Here is the code for Snell.hpp
#ifndef Snell_hpp
#define Snell_hpp
#include <iostream>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <string>
#include <algorithm>
#include <cmath>
using namespace std;
class Snell{
private:
double GetV(double lat,double dep);
int ny,nz,time;
double la[30],h[20],v[10][30];
double lat,alt,step;
public:
Snell();
void Open(string filename);
double Locate(int i);
double angle_tr;
};
#endif /* Snell_hpp */
and Snell.cpp:
#include "Snell.hpp"
Snell::Snell(){
ny=1,nz=3,time=0;
lat=0,alt=0,step=1;
angle_tr=M_PI/2;
}
void Snell::Open(string filename){
ifstream fin(filename);
stringstream ss;
string str,tok;
for (int i=0; i<nz; i++) {
(getline(fin, str));
ss.str(str);
for (int j=0; j<ny; j++) {
getline(ss, tok, ',');
v[i][j]=stod(tok);
cout<<v[i][j]<<",i="<<i<<",j="<<j<<endl;
}
ss.clear();
}
fin.close();
angle_tr=v[1][0]/v[0][0];
}
double Snell::GetV(double lat, double dep){
int index_la = 0,index_dep = 0;
index_dep=round(dep);
return (v[index_dep][index_la]+v[index_dep+1][index_la])/2;
}
double Snell::Locate(int i){
string filename;
double count_t=0;
double latt=lat,altt=alt,step_altt_all=0,angle=0,angle_p=0;
double vsy,vsz;
double vs,vs_n;
ofstream fout;
angle=M_PI/2-atan(angle_tr);
vs=GetV(lat, alt);
filename="Test"+to_string(i)+"_"+to_string(time)+".txt";
fout.open(filename,ios::out);
fout<<lat<<","<<alt<<endl;
while (altt!=2) {
//cout<<"Compute Velocity in each dimension"<<endl;
angle_p=angle;
vsy=vs*cos(angle);
vsz=vs*sin(angle);
//cout<<"Check Velocity"<<endl;
if (vsy==0||vsz==0) {
break;
}
//cout<<"Compute reflection point"<<endl;
step_altt_all=step/vsz;
count_t=count_t+step/vsz;//time plus one
latt=latt+vsy*(step_altt_all);
step_altt_all=0;
altt=altt+step;
//cout<<"Compute New Velocity"<<endl;
vs_n=GetV(latt,altt);
if ((vs_n*cos(angle)/vs)>1) {
break;
}
else{
angle=M_PI/2-asin(vs_n*cos(angle)/vs);
vs=vs_n;
if (angle!=angle_p)
fout<</*"position:"<<*/latt<<","<<altt<<endl;
}
}
fout.close();
filename="Result"+to_string(i)+"_"+to_string(time)+".txt";
fout.open(filename);
fout<<0<<" "<<latt<<" "<<altt<<" "<<step<<endl;
fout.close();
return count_t;
}
My immediate guess is: You must have blown your stack. Please see why is stack memory size so limited?
....And yes, On my platform, my guess was correct...
Reproducing your program, but modifying your main.cpp ...
int main(int argc, const char * argv[]){//thread 1 exc_bad_access (code=2 address=0x7fff5f238304)
string filename;
double time;
//Snell S[3600];
std::cout << sizeof(Snell) << " bytes" << std::endl;
return 0;
}
It gives an output of
2848 bytes
....And You are trying to allocate 3600 of them... ~10MB!!
The solution to that is to allocate it on the heap using a std::unique_ptr or better still, your good friend, std::vector.
Modify your main to this
#include <string>
#include <memory>
//or #include <vector>
#include "Snell.hpp"
int main(int argc, const char * argv[]){//thread 1 exc_bad_access (code=2 address=0x7fff5f238304)
string filename;
double time;
std::unique_ptr<S[]> p(new Snell[3600]);
//or std::vector<Snell> S(3600);
for (int i=1; i<=1; i++) {
while (S[i].angle_tr>0) {
filename="VPVSMOD"+to_string(i)+".txt";
S[i].Open(filename);
time=S[i].Locate(i);
cout<<"The "<<i<<"th event takes "<<time<<" seconds to reach the destination"<<endl;
S[i].angle_tr-=0.01;
}
}
return 0;
}
I have an input file that looks like this
1 0 3
2 11 5
3 15 1
4 16 11
and a structure that looks like this
struct numb {
int numb1;
int numb2;
int numb3;
}
and I need to create an array of the struct so that each element of the array holds all three numbers. So
numbArray[0].numb1 == 1
numbArray[0].numb2 == 0
numbArray[0].numb3 == 3
numbArray[1].numb1 == 2
numbArray[1].numb2 == 11
and so on. I've gotten the hang of opening and closing files, finding how many lines there are in a file, and reading a single line from a file, but I do not know how to store individual elements from a line.
My program looks like this so far:
#include <iostream>
#include <fstream>
#include <string>
int main(int argc, char* argv[])
{
ifstream inFile(argv[1]);
int fileLength = 0;
std::string line;
while(std::getline(inFile, line))
{
++fileLength;
}
struct numb {
int numb1;
int numb2;
int numb3;
}
if(inFile.is_open())
{
for(unsigned i = 0; i <= fileLength; i++)
{
//What to do here?
}
}
}
Use getline when you don't have regular structure to the input and need to handle variation between lines. When your input file has regular structure (in this case, there are always three values per line), then simply use the stream extraction operators directly:
#include <iostream>
#include <vector>
struct group
{
int n1;
int n2;
int n3;
};
int main()
{
std::vector<group> groups;
while (std::cin)
{
group line;
line.n1 << std::cin;
line.n2 << std::cin;
line.n3 << std::cin;
groups.push_back(group);
}
}
Express your ideas directly in code as much as possible.
Note I've written the code assuming that the file is in the proper form. If there are too many or too few values per line, then the above code will be confused. However, it is best to code the simplest thing that could possibly work and worry about complexity when you need it. In your example you stated that the input file was well-formed, so there's no need to overcomplicate things.
I recommend using a std::stringstream for this:
#include <iostream>
#include <sstream>
#include <string>
#include <stdio.h>
#include <vector>
struct numb {
int numb1;
int numb2;
int numb3;
};
void populate(std::vector<numb>& my_numbs, std::string line) {
std::stringstream ss(line);
numb my_numb;
ss >> my_numb.numb1 >> my_numb.numb2 >> my_numb.numb3;
my_numbs.push_back(my_numb);
}
void output(const numb my_numbs) {
printf("%d %d %d\n", my_numbs.numb1, my_numbs.numb2, my_numbs.numb3);
}
int main(int argc, char* argv[]) {
ifstream inFile(argv[1]);
std::string line;
std::vector<numb> my_vect;
while(std::getline(inFile, line)) {
populate(my_vect, line);
}
for(size_t i = 0; i < my_vect.size(); ++i) {
std::cout << "my_vect[" << i << "]:";
output(my_vect[i]);
}
return 0;
}
std::stringstreams allow you to parse out data types from std::strings, you you just need to parse out 3 ints, which you can use with your struct. You then push the struct into your vector.
Here's the working ideone taking input from stdin.
You should probably be able to do something like this:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main(int argc, char* argv[])
{
ifstream inFile(argv[1]);
int fileLength = 0;
std::string line;
struct numb {
int numb1;
int numb2;
int numb3;
};
vector<vector<int>> sets;
int n1, n2, n3;
while (std::cin >> n1)
{
cin >> n2;
cin >> n3;
vector<int> vec;
vec.push_back(n1);
vec.push_back(n2);
vec.push_back(n3);
sets.push_back(vec);
}
numb * numbSet = new numb[sets.size()];
//Since the vectors data is continuous in memory just as the array of structs are
//you can just copy the data directly
for (int i = 0; i < sets.size(); i++)
{
std::memcpy(&numbSet[i], &sets[i][0], sizeof(numb));
}
}
make a function which receive the file name but it not working properly because it receives "Doctor.txtG" but I am giving "Doctor.txt" how can i resolve it?My code is Given below......
#include <iostream>
#include <conio.h>
#include <fstream>
using namespace std;
int number_of_lines = 0;
int numberoflines(string A);
int main()
{
cout<<numberoflines("Doctor.txt");
getch();
return 0;
}
int numberoflines(string A)
{
int Len;
char Chr[Len];
Len=A.length();
A.copy(Chr, Len);
//cout<<Len;
cout<<Chr;
string line;
ifstream myfile(Chr);
if(myfile.is_open())
{
while(!myfile.eof())
{
getline(myfile,line);
number_of_lines++;
}
myfile.close();
}
return number_of_lines;
}
It needs to copy a null-terminated byte into Chr.
Use
strcpy(Chr, A.c_str());
instead of A.copy(Chr, Len);
And you should properly init Chr like
char Chr[1024]
or
char* Chr = new char[Len + 1].
Your problem is happening because you are trying to create a char array with the size Len. But you have not initialized Len before using it. This is why it is resulting in undefined behavior and creating this problem. Always try to initialize variables when you declare them. Otherwise, this problem will happen quite often.
However, You don't need to create another char array. Just use std::string::c_str(); in your parameter for the constructor of the ifstream. I am giving a sample code below. This should solve your problem.
#include <iostream>
#include <conio.h>
#include <fstream>
using namespace std;
int number_of_lines = 0;
int numberoflines(string A);
int main()
{
cout<<numberoflines("Doctor.txt");
getch();
return 0;
}
int numberoflines(string A)
{
string line;
ifstream myfile(A.c_str());
if(myfile.is_open())
{
while(!myfile.eof())
{
getline(myfile,line);
number_of_lines++;
}
myfile.close();
}
return number_of_lines;
}