I have written a program to read a CSV file but I'm having some trouble in extracting data from that CSV file in c++. I want to count the no. of columns starting from the 5th column in the 1st row until the last column of the 1st row of the CSV file. I have written the following code to read a CVS file, but I am not sure how shall I count the no. of columns as I have mentioned before.
Will appreciate it if anyone could please tell me how shall I go about it?
char* substring(char* source, int startIndex, int endIndex)
{
int size = endIndex - startIndex + 1;
char* s = new char[size+1];
strncpy(s, source + startIndex, size); //you can read the documentation of strncpy online
s[size] = '\0'; //make it null-terminated
return s;
}
char** readCSV(const char* csvFileName, int& csvLineCount)
{
ifstream fin(csvFileName);
if (!fin)
{
return nullptr;
}
csvLineCount = 0;
char line[1024];
while(fin.getline(line, 1024))
{
csvLineCount++;
};
char **lines = new char*[csvLineCount];
fin.clear();
fin.seekg(0, ios::beg);
for (int i=0; i<csvLineCount; i++)
{
fin.getline(line, 1024);
lines[i] = new char[strlen(line)+1];
strcpy(lines[i], line);
};
fin.close();
return lines;
}
I have attached a few lines from the CSV file:-
Province/State,Country/Region,Lat,Long,1/22/20,1/23/20,1/24/20,
,Afghanistan,33.0,65.0,0,0,0,0,0,0,0,
,Albania,41.1533,20.1683,0,0,0,0
What I need is, in the 1st row, the number of dates after Long.
To answer your question:
I have attached a few lines from the CSV file:-
Province/State,Country/Region,Lat,Long,1/22/20,1/23/20,1/24/20, ,Afghanistan,33.0,65.0,0,0,0,0,0,0,0, ,Albania,41.1533,20.1683,0,0,0,0
What I need is, in the 1st row, the number of dates after Long.
Yeah, not that difficult - that's how I would do it:
#include <iostream>
#include <string>
#include <fstream>
#include <regex>
#define FILENAME "test.csv" //Your filename as Macro
//(The compiler just sees text.csv instead of FILENAME)
void read(){
std::string n;
//date format pattern %m/%dd/%YY
std::regex pattern1("\\b\\d{1}[/]\\d{2}[/]\\d{2}\\b");
//date format pattern %mm/%dd/%YY
std::regex pattern2("\\b\\d{2}[/]\\d{2}[/]\\d{2}\\b");
std::smatch result1, result2;
std::ifstream file(FILENAME, std::ios::in);
if ( ! file.is_open() )
{
std::cout << "Could not open file!" << '\n';
}
do{
getline(file,n,',');
//https://en.cppreference.com/w/cpp/string/basic_string/getline
if(std::regex_search(n,result1,pattern1))
std::cout << result1.str(1) << n << std::endl;
if(std::regex_search(n,result2,pattern2))
std::cout << result2.str(1) << n << std::endl;
}
while(!file.eof());
file.close();
}
int main ()
{
read();
return 0;
}
The file test.csv contains the following for testing:
Province/State,Country/Region,Lat,Long,1/22/20,1/23/20,1/24/20, ,Afghanistan,33.0,65.0,0,0,0,0,0,0,0, ,Albania,41.1533,20.1683,0,0,0,0
Province/State,Country/Region,Lat,Long,1/25/20,12/26/20,1/27/20, ,Bfghanistan,33.0,65.0,0,0,0,0,0,0,0, ,Blbania,41.1533,20.1683,0,0,0,0
It actually is pretty simple:
getline takes the open file and "escapes" at a so called escape-charachter,
in your case a comma ','.
(That is the very best way I found in reading csv - you can replace it with whatever you want, for example: ';' or ' ' or '...' - guess you get the drill)
After this you got all data nicely separated underneath one another without a comma.
Now you can "filter" out what you need. I use regex - but use what ever you want.
(Just fyi: For c++ tagged questions you shouldn't use c-style like strncpy..)
I gave you an example for 1.23.20 (m/dd/yy) and to make it simple if your file contains a november or december like 12.22.20 (mm/dd/yy) to make
the regex pattern more easy to read/understand in 2 lines.
you can/may have to expand the regex pattern if the data somehow matches
your date format in the file, really good explained here and not as complicated as it looks.
From that point you can put all the printed stuff f.e. in a vector (some more convenient array) to handle and/or pass/return data - that's up to you.
If you need more explaining I am happy to help you out and/or expand this example, just leave a comment.
You basically want to search for the seperator substring within your line (normally it is ';').
If you print out your lines it should look like this:
a;b;c;d;e;f;g;h
There are several ways to achieve what you want, I would look for a strip or split upon character function. Something along the example below should work. If you use std you can go with str.IndexOf instead of a loop.
int rows(char* line,char seperator, int count) {
unsigned length = strlen(line);
for (int i=pos; i<length;i++){
if(strcmp(line[i],seperator)) break;
}
count++;
if (i<length-1) return rows(substring(line,i,length-i),seperator,count);
else return count;
}
The recursion can obviously be replaced by one loop ;)
int countSign(char* line, char* sign){
unsigned l = strlen(line);
int count = 0;
for (int i=0; i < l; i++) {
if(strcmp(line[i],sign)) count++;
}
}
This assignment is called a co-currence problem. The point of my program is to read in sentences from a file and ignore any punctuation. Then, I will read user input where the user will enter words separated by a space only and I have to search for those exact words in all the sentences of the file and return the line number where all the words are found.
My approach now is to create a pointer array to other arrays that contain the words for each sentence.
ifstream read;
string filename;
string **txtPtr = nullptr;
int numLines = 0;
getFileName();
getNumLines(read, fileName); //stores # of lines into numLines
txtPtr = new string*[numLines];
My question is, can I pass the pointer to a function as string *lines or string *lines[]?
I would parse the input file and build an index, and then I would look up user-entered words in that index. The index would be std::map with std::string as a key and with "Entry" struct as a value:
struct Entry {
int line;
int sentence;
};
typedef std::map<std::string, Entry> Index;
This is how insertion would look like:
Index index;
Entry val;
val.line = 1;
val.sentence = 2;
std::string word = "hi";
index.insert(Index::value_type(word, val));
This is how lookup would look like:
Index::iterator it = index.find(word);
if (it != index.end())
std::cout << "found:" << it->second.line;
I know it's not the answer for your question, but it might help anyway..
I have a situation where I loop through the first 64 lines of a file and save each line into a string. The rest of the file is unknown. It may be a single line or many.
I know that there will be 64 lines at the beginning of the file but I do not know their size.
How can I save the entirety of the rest of the file to a string?
This is what I currently have:
std::ifstream signatureFile(fileName);
for (int i = 0; i < 64; ++i) {
std::string tempString;
//read the line
signatureFile >> tempString;
//do other processing of string
}
std::string restOfFile;
//save the rest of the file into restOfFile
Thanks to the responses this is how I got it working:
std::ifstream signatureFile(fileName);
for (int i = 0; i < 64; ++i) {
std::string tempString;
//read the line
//using getline prevents extra line break when reading the rest of file
std::getline(signatureFile, tempString);
//do other processing of string
}
//save the rest of the file into restOfFile
std::string restOfFile{ std::istreambuf_iterator<char>{signatureFile},
std::istreambuf_iterator<char>{} };
signatureFile.close();
One of std::string's constructors is a template that takes two iterators as parameters, a beginning and an ending iterator, and constructs a string from the sequence defined by the iterators.
It just so happens that std::istreambuf_iterator provides a suitable input iterator for iterating over the contents of an input stream:
std::string restOfFile{std::istreambuf_iterator<char>{signatureFile},
std::istreambuf_iterator<char>{}};
You can use string buffer.
#include <sstream>
// ...
stringbuf buf;
signatureFile.get(buf);
string restOfFile = buf.str();
So, I came up wit the following code to open a text file and save it in and use an array to print out all the text. My question is, how can I access a specific word or text in the file. If I am not mistaken there should be a for loop involved in this, but I am not quite sure how to go about doing it.
int main() {
ifstream dictionaryFile;
dictionaryFile.open("dictionary.txt");
char output[100];
//char wordsFromDictionary[40437][22];
int i=0;
if(dictionaryFile.is_open()){
while(!dictionaryFile.eof()){
dictionaryFile >> output;
cout<<output<<endl;
}
}
return 0;
}
If you want to read in some strings, the obvious choice would be to use std::strings to do the job. If you want an array of them, store them in an std::vector:
ifstream d("dictionary.txt");
std::vector<std::string> words{std::istream_iterator<std::string>(d), {}};
This reads all the words into the vector. If they're already sorted, you can then (for example) use std::binary_search to find whether a word is in the vector or not.
As you have a char array
char output[100];
there is no distinction between words in this data structure. File was simply read character by character and stored in the array.
A simple implementation of separation into words (using loops as you requested, with minimal changes to your code), assuming words are separated by a delimiter would be
char wordsFromDictionary[40437][22];
char delimiter=...
int i=0;
int j=0
char c;
if(dictionaryFile.is_open()){
while(!dictionaryFile.eof()){
c=dictionaryFile.get();
if(c==delimiter){
i++;
j=0;
}
else if(j<22) {
wordsFromDictionary[i][j]=c;
j++;
}
}
}
Note that this simply cuts, shortens the words that are longer than 22 chars.
I need to read the nth line of a text file (e.g. textfile.findline(0) would find the first line of the text file loaded with ifstream textfile). Is this possible?
I don't need to put the contents of the file in an array/vector, I need to just assign a specific line of the text file to a varible (specifically a int).
P.S. I am looking for the simplest solution that would not require me to use any big external library (e.g. Boost)
Thanks in advance.
How about this?
std::string ReadNthLine(const std::string& filename, int N)
{
std::ifstream in(filename.c_str());
std::string s;
//for performance
s.reserve(some_reasonable_max_line_length);
//skip N lines
for(int i = 0; i < N; ++i)
std::getline(in, s);
std::getline(in,s);
return s;
}
If you want to read the start of the nth line, you can use stdin::ignore to skip over the first n-1 lines, then read from the next line to assign to the variable.
template<typename T>
void readNthLine(istream& in, int n, T& value) {
for (int i = 0; i < n-1; ++i) {
in.ignore(numeric_limits<streamsize>::max(), '\n');
}
in >> value;
}
Armen's solution is the correct answer, but I thought I'd throw out an alternative, based on jweyrich's caching idea. For better or for worse, this reads in the entire file at construction, but only saves the newline positions (doesn't store the entire file, so it plays nice with massive files.) Then you can simply call ReadNthLine, and it will immediately jump to that line, and read in the one line you want. On the other hand, this is only optimal if you want to get only a fraction of the lines at a time, and the line numbers are not known at compile time.
class TextFile {
std::ifstream file_stream;
std::vector<std::ifstream::streampos> linebegins;
TextFile& operator=(TextFile& b) = delete;
public;
TextFile(std::string filename)
:file_stream(filename)
{
//this chunk stolen from Armen's,
std::string s;
//for performance
s.reserve(some_reasonable_max_line_length);
while(file_stream) {
linebegins.push_back(file_stream.tellg());
std::getline(file_stream, s);
}
}
TextFile(TextFile&& b)
:file_stream(std::move(b.file_stream)),
:linebegins(std::move(b.linebegins))
{}
TextFile& operator=(TextFile&& b)
{
file_stream = std::move(b.file_stream);
linebegins = std::move(b.linebegins);
}
std::string ReadNthLine(int N) {
if (N >= linebegins.size()-1)
throw std::runtime_error("File doesn't have that many lines!");
std::string s;
// clear EOF and error flags
file_stream.clear();
file_stream.seekg(linebegins[N]);
std::getline(file_stream, s);
return s;
}
};
It's certainly possible. There are (n-1) '\n' characters preceding the nth line. Read lines until you reach the one you're looking for. You can do this on the fly without storing anything except the current line being considered.