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;
}
Related
I'm currently writting a program where I try to filter extra spaces so if there are more than 1 spaces in a row, I discard the rest leaving only one
But this is only the first step because the aim of the program is to parse a txt file with mips assembly instructions.
So far I've opened the file, stored the content in a vector and then stored the vector content in an array. Then I check, if you find a char 2 times in a row shift the array to the left.
The problem is that the code works well for any other letter, except for the space character. (On the code below I test it with the 'D' character and it works)
#include <iostream>
#include <cmath>
#include <fstream>
#include <cstdlib>
#include <vector>
#include <algorithm>
using namespace std;
class myFile {
vector<string> myVector;
public:
void FileOpening();
void file_filter();
};
void myFile::FileOpening() {
string getcontent;
ifstream openfile; //creating an object so we can open files
char filename[50];
int i = 0;
cout << "Enter the name of the file you wish to open: ";
cin.getline(filename, 50); //whatever name file the user enters, it's going to be stored in filename
openfile.open(filename); //opening the file with the object I created
if (!openfile.is_open()) //if the file is not opened, exit the program
{
cout << "File is not opened! Exiting the program.";
exit(EXIT_FAILURE);
};
while (!openfile.eof()) //as long as it's not the end of the file do..
{
getline(openfile, getcontent); //get the whole text line and store it in the getcontent variable
myVector.push_back(getcontent);
i++;
}
}
void myFile::file_filter() {
unsigned int i = 0, j = 0, flag = 0, NewLineSize, k, r;
string Arr[myVector.size()];
for (i = 0; i < myVector.size(); i++) {
Arr[i] = myVector[i];
}
//removing extra spaces,extra line change
for (i = 0; i < myVector.size(); i++) {
cout << "LINE SIZE" << myVector[i].size() << endl;
for (j = 0; j < myVector[i].size(); j++) {
//If I try with this character for example,
//it works (Meaning that it successfully discards extra 'Ds' leaving only one.
// But if I replace it with ' ', it won't work. It gets out of the loop as soon
//as it detects 2 consecutive spaces.
if ((Arr[i][j] == 'D') && (Arr[i][j + 1] == 'D')) {
for (k = j; k < myVector[i].size(); k++) {
Arr[i][k] = Arr[i][k + 1];
flag = 0;
j--;
}
}
}
}
for (i = 0; i < myVector.size(); i++) {
for (j = 0; j < myVector[i].size(); j++) //edw diapernw tin kathe entoli
{
cout << Arr[i][j];
}
}
}
int main() {
myFile myfile;
myfile.FileOpening();
myfile.file_filter();
}
My question is, why does it work with all the characters except the space one, and how do I fix this?
Thanks in advace.
Wow. Many lines of code. I can only recomend to learn more about the STL and algorithms.
You can read the complete file into a vector using the vectors "range"-constructor and std::istream_iterator. Then you can replace one or more spaces in a string by using a std::regex. This is really not complicated.
In the below example, I do all the work, with 2 lines of code in function main. Please have a look:
#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
#include <string>
#include <fstream>
#include <regex>
using LineBasedTextFile = std::vector<std::string>;
class CompleteLine { // Proxy for the input Iterator
public:
// Overload extractor. Read a complete line
friend std::istream& operator>>(std::istream& is, CompleteLine& cl) { std::getline(is, cl.completeLine); return is; }
// Cast the type 'CompleteLine' to std::string
operator std::string() const { return completeLine; }
protected:
// Temporary to hold the read string
std::string completeLine{};
};
int main()
{
// Open the input file
std::ifstream inputFile("r:\\input.txt");
if (inputFile)
{
// This vector will hold all lines of the file. Read the complete file into the vector through its range constructor
LineBasedTextFile text{ std::istream_iterator<CompleteLine>(inputFile), std::istream_iterator<CompleteLine>() };
// Replace all "more-than-one" spaces by one space
std::for_each(text.begin(), text.end(), [](std::string& s) { s = std::regex_replace(s, std::regex("[\\ ]+"), " "); });
// For Debug purposes. Print Result to std::out
std::copy(text.begin(), text.end(), std::ostream_iterator<std::string>(std::cout, "\n"));
}
return 0;
}
I hope, I could give you some idea on how to proceed.
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));
}
}
I have written a program to store a text file in vector of characters .
#include<iostream>
#include<fstream>
#include <algorithm>
#include<vector>
using namespace std;
int main()
{
vector<char> vec;
ifstream file("text.txt");
if(!file.eof() && !file.fail())
{
file.seekg(0, std::ios_base::end);
std::streampos fileSize = file.tellg();
vec.resize(fileSize);
file.seekg(0, std::ios_base::beg);
file.read(&vec[0], fileSize);
}
int c = count(vec.begin(), vec.end(), 'U');
cout << c;
return 0;
}
I want to count occurrence of "USER" in the text file , but using count i can only count number of characters . How can i count number of occurrences of "USER" in the vector of character?
For example
text.txt
USERABRUSER#$$* 34 USER ABC RR IERUSER
Then the count of "USER" is 4. Words can only be in uppercase.
std::string has a find member function that will find an occurrence of one string inside another. You can use that to count occurrences something like this:
size_t count(std::string const &haystack, std::string const &needle) {
auto occurrences = 0;
auto len = needle.size();
auto pos = 0;
while (std::string::npos != (pos = haystack.find(needle, pos))) {
++occurrences;
pos += len;
}
return occurrences;
}
For example:
int main() {
std::string input{ "USERABRUSER#$$* 34 USER ABC RR IERUSER" };
std::cout << count(input, "USER");
}
...produces an output of 4.
This is how I would do it:
#include <fstream>
#include <sstream>
#include <iostream>
#include <unordered_map>
#include <string>
using namespace std;
int main() {
unordered_map<string, size_t> data;
string line;
ifstream file("text.txt");
while (getline(file, line)) {
istringstream is(line);
string word;
while (is >> word) {
++data[word];
}
}
cout << data["USER"] << endl;
return 0;
}
Let's try again. Once again, a vector isn't necessary. This is what I would consider to be the most C++ idiomatic way. It uses std::string's find() method to repeatedly find the substring in order until the end of the string is reached.
#include <fstream>
#include <iostream>
#include <string>
int main() {
// Read entire file into a single string.
std::ifstream file_stream("text.txt");
std::string file_contents(std::istreambuf_iterator<char>(file_stream),
std::istreambuf_iterator<char>());
unsigned count = 0;
std::string substr = "USER";
for (size_t i = file_contents.find(substr); i != std::string::npos;
i = str.find(substr, i + substr.length())) {
++count;
}
}
#include <iostream>
#include <string>
#include <vector>
/*
Using STL's string class because the problem does not refer any
limits regarding the number of characters per line.
*/
using namespace std;
int main()
{
string line;
vector<string> lines;
while (getline(cin, line))
{
lines.push_back(line);
}
unsigned int i, u;
unsigned int opening = 1; // 2 if last was opening, 1 if it was closing
for (i = 0; i < (int) lines.size(); i++)
{
for (u = 0; u < (int) lines[u].length(); u++)
{
}
}
return 0;
}
I have that simple code that just reads over a few lines (input file):
"To be or not to be," quoth the Bard, "that
is the question".
The programming contestant replied: "I must disagree.
To `C' or not to `C', that is The Question!"
However, I found that it is SEGFAULTing as it reads a ' ' (space) character on the first line (4th character):
(gdb) run < texquotes_input.txt
Starting program: /home/david/src/oni/texquotes < texquotes_input.txt
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b92533 in std::string::length() const () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
I really can't understand why, I'm not doing anything inside the loop, I'm just looping.
I already found the problem. It's the inner loop:
for (u = 0; u < (int) lines[u].length(); u++)
{
}
Should be:
for (u = 0; u < (int) lines[i].length(); u++)
{
}
In another answer the index typo was already spotted.
I'd like to add that using range-based for loops those kinds of problems are more difficult to happen, since the loop is kind of more "implicit":
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string line;
vector<string> lines;
while (getline(cin, line))
{
lines.push_back(line);
}
for ( const auto& currLine : lines )
{
for ( auto ch : currLine )
{
cout << ch;
}
cout << '\n';
}
}
Using if and while/do-while, my job is to print following user's inputs (string value) in reverse order.
For example:
input string value : "You are American"
output in reverse order : "American are You"
Is there any way to do this?
I have tried
string a;
cout << "enter a string: ";
getline(cin, a);
a = string ( a.rbegin(), a.rend() );
cout << a << endl;
return 0;
...but this would reverse the order of the words and spelling while spelling is not what I'm going for.
I also should be adding in if and while statements but do not have a clue how.
The algorithm is:
Reverse the whole string
Reverse the individual words
#include<iostream>
#include<algorithm>
using namespace std;
string reverseWords(string a)
{
reverse(a.begin(), a.end());
int s = 0;
int i = 0;
while(i < a.length())
{
if(a[i] == ' ')
{
reverse(a.begin() + s, a.begin() + i);
s = i + 1;
}
i++;
}
if(a[a.length() - 1] != ' ')
{
reverse(a.begin() + s, a.end());
}
return a;
}
Here is a C-based approach that will compile with a C++ compiler, which uses the stack to minimize creation of char * strings. With minimal work, this can be adapted to use C++ classes, as well as trivially replacing the various for loops with a do-while or while block.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LINE_LENGTH 1000
#define MAX_WORD_LENGTH 80
void rev(char *str)
{
size_t str_length = strlen(str);
int str_idx;
char word_buffer[MAX_WORD_LENGTH] = {0};
int word_buffer_idx = 0;
for (str_idx = str_length - 1; str_idx >= 0; str_idx--)
word_buffer[word_buffer_idx++] = str[str_idx];
memcpy(str, word_buffer, word_buffer_idx);
str[word_buffer_idx] = '\0';
}
int main(int argc, char **argv)
{
char *line = NULL;
size_t line_length;
int line_idx;
char word_buffer[MAX_WORD_LENGTH] = {0};
int word_buffer_idx;
/* set up line buffer - we cast the result of malloc() because we're using C++ */
line = (char *) malloc (MAX_LINE_LENGTH + 1);
if (!line) {
fprintf(stderr, "ERROR: Could not allocate space for line buffer!\n");
return EXIT_FAILURE;
}
/* read in a line of characters from standard input */
getline(&line, &line_length, stdin);
/* replace newline with NUL character to correctly terminate 'line' */
for (line_idx = 0; line_idx < (int) line_length; line_idx++) {
if (line[line_idx] == '\n') {
line[line_idx] = '\0';
line_length = line_idx;
break;
}
}
/* put the reverse of a word into a buffer, else print the reverse of the word buffer if we encounter a space */
for (line_idx = line_length - 1, word_buffer_idx = 0; line_idx >= -1; line_idx--) {
if (line_idx == -1)
word_buffer[word_buffer_idx] = '\0', rev(word_buffer), fprintf(stdout, "%s\n", word_buffer);
else if (line[line_idx] == ' ')
word_buffer[word_buffer_idx] = '\0', rev(word_buffer), fprintf(stdout, "%s ", word_buffer), word_buffer_idx = 0;
else
word_buffer[word_buffer_idx++] = line[line_idx];
}
/* cleanup memory, to avoid leaks */
free(line);
return EXIT_SUCCESS;
}
To compile with a C++ compiler, and then use:
$ g++ -Wall test.c -o test
$ ./test
foo bar baz
baz bar foo
This example unpacks the input string one word at a time,
and builds an output string by concatenating in reverse order.
`
#include <iostream>
#include <sstream>
using namespace std;
int main()
{
string inp_str("I am British");
string out_str("");
string word_str;
istringstream iss( inp_str );
while (iss >> word_str) {
out_str = word_str + " " + out_str;
} // while (my_iss >> my_word)
cout << out_str << endl;
return 0;
} // main
`
This uses exactly one each of if and while.
#include <string>
#include <iostream>
#include <sstream>
void backwards(std::istream& in, std::ostream& out)
{
std::string word;
if (in >> word) // Read the frontmost word
{
backwards(in, out); // Output the rest of the input backwards...
out << word << " "; // ... and output the frontmost word at the back
}
}
int main()
{
std::string line;
while (getline(std::cin, line))
{
std::istringstream input(line);
backwards(input, std::cout);
std::cout << std::endl;
}
}
You might try this solution in getting a vector of string's using the ' ' (single space) character as a delimiter.
The next step would be to iterate over this vector backwards to generate the reverse string.
Here's what it might look like (split is the string splitting function from that post):
Edit 2: If you don't like vectors for whatever reason, you can use arrays (note that pointers can act as arrays). This example allocates a fixed size array on the heap, you may want to change this to say, double the size when the current word amount has reached a certain value.
Solution using an array instead of a vector:
#include <iostream>
#include <string>
using namespace std;
int getWords(string input, string ** output)
{
*output = new string[256]; // Assumes there will be a max of 256 words (can make this more dynamic if you want)
string currentWord;
int currentWordIndex = 0;
for(int i = 0; i <= input.length(); i++)
{
if(i == input.length() || input[i] == ' ') // We've found a space, so we've reached a new word
{
if(currentWord.length() > 0)
{
(*output)[currentWordIndex] = currentWord;
currentWordIndex++;
}
currentWord.clear();
}
else
{
currentWord.push_back(input[i]); // Add this character to the current word
}
}
return currentWordIndex; // returns the number of words
}
int main ()
{
std::string original, reverse;
std::getline(std::cin, original); // Get the input string
string * arrWords;
int size = getWords(original, &arrWords); // pass in the address of the arrWords array
int index = size - 1;
while(index >= 0)
{
reverse.append(arrWords[index]);
reverse.append(" ");
index--;
}
std::cout << reverse << std::endl;
return 0;
}
Edit: Added includes, main function, while loop format
#include <vector>
#include <string>
#include <iostream>
#include <sstream>
// From the post
std::vector<std::string> &split(const std::string &s, char delim, std::vector<std::string> &elems)
{
std::stringstream ss(s);
std::string item;
while(std::getline(ss, item, delim)) {
elems.push_back(item);
}
return elems;
}
std::vector<std::string> split(const std::string &s, char delim) {
std::vector<std::string> elems;
return split(s, delim, elems);
}
int main ()
{
std::string original, reverse;
std::cout << "Input a string: " << std::endl;
std::getline(std::cin, original); // Get the input string
std::vector<std::string> words = split(original, ' ');
std::vector<std::string>::reverse_iterator rit = words.rbegin();
while(rit != words.rend())
{
reverse.append(*rit);
reverse.append(" "); // add a space
rit++;
}
std::cout << reverse << std::endl;
return 0;
}
This code here uses string libraries to detect the blanks in the input stream and rewrite the output sentence accordingly
The algorithm is
1. Get the input stream using getline function to capture the spacecs. Initialize pos1 to zero.
2. Look for the first space in the input stream
3. If no space is found, the input stream is the output
4. Else, get the position of the first blank after pos1, i.e. pos2.
5. Save the sub-string bewteen pos1 and pos2 at the beginning of the output sentence; newSentence.
6. Pos1 is now at the first char after the blank.
7. Repeat 4, 5 and 6 untill no spaces left.
8. Add the last sub-string to at the beginning of the newSentence. –
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string sentence;
string newSentence;
string::size_type pos1;
string::size_type pos2;
string::size_type len;
cout << "This sentence rewrites a sentence backward word by word\n"
"Hello world => world Hello"<<endl;
getline(cin, sentence);
pos1 = 0;
len = sentence.length();
pos2 = sentence.find(' ',pos1);
while (pos2 != string::npos)
{
newSentence = sentence.substr(pos1, pos2-pos1+1) + newSentence;
pos1 = pos2 + 1;
pos2 = sentence.find(' ',pos1);
}
newSentence = sentence.substr(pos1, len-pos1+1) + " " + newSentence;
cout << endl << newSentence <<endl;
return 0;
}