I am not a programmer, but am an engineer who needs to use C++ coding on this occasion, so sorry if this question is a little basic.
I need to use a look up table as I have some highly non-linear dynamics going on that I need to model. It consists of literally 1000 paired values, from a pair of (0.022815, 0.7) up to (6.9453, 21.85).
I don't want to have to type all these values out in my C code. The values are currently stored in Matlab. Can I read them from a .dat file or something similar?
I will have calculated a value and simply want the program to kick out the paired value.
Thanks,
Adam
You can't read something stored in Matlab directly, unless you want to
write a parser for whatever format Matlab stores its data in. I'm not
familiar with Matlab, but I would be very surprised if it didn't have a
function to output this data to a file, in some text format, which you
could read and parse.
Assuming this is constant data, if it could output something along the
lines of:
{ 0.022815, 0.7 },
...
{ 6.9453, 21.85 },
you could include it as the initializer of a table in C++. (It may look
strange to have a #include in the middle of a variable definition, but
it's perfectly legal, and in such cases, perfectly justified.) Or just
copy/paste it into your C++ program.
If you can't get exactly this format directly, it should be trivial to
write a small script that would convert whatever format you get into
this format.
this program defines a map, then reading from a.txt file, inserting to a map, iterating on map for any purposes you have, and finally writing the map into a file.
just a simple practice:
#include <fstream>
#include <iostream>
#include <map>
using namespace std;
int main(){
ifstream inFile("a.txt", ios::in);
if (! inFile ){
cout<<"unabl to open";
return 0;
}
//reading a file and inserting in a map
map<double,double> mymap;
double a,b;
while( ! inFile.eof() ){
inFile>>a>>b;
mymap.insert ( a,b );
}
inFile.close(); //be sure to close the file
//iterating on map
map<double,double>::iterator it;
for ( it=mymap.begin() ; it != mymap.end(); it++ ){
// (*it).first
// (*it).second
}
//writing the map into a file
ofstream outFile;
outFile.open ("a.txt", ios::out); // or ios::app if you want to append
for ( it=mymap.begin() ; it != mymap.end(); it++ ){
outFile << (*it).first << " - " << (*it).second << endl; //what ever!
}
outFile.close();
return 0;
}
What I would do for this is as follows as I think this is faster than file open and close. First of all create a header file which contains all the data in an array. You could you a "replace all" available in Notepad or so to replace the () braces to { } braces. Later on you could even write a script that makes the header file from the Matlab file
>> cat import_data.h
#define TBL_SIZE 4 // In your case it is 1000
const double table[TBL_SIZE][2] =
{
{ 0.022815, 0.7 },
{ 6.9453, 21.85 },
{ 4.666, 565.9},
{ 567.9, 34.6}
};
Now in the main program you include this header also for the data
>> cat lookup.c
#include <stdio.h>
#include "import_data.h"
double lookup(double key)
{
int i=0;
for(;i<TBL_SIZE; i++) {
if(table[i][0] == key)
return table[i][1];
}
return -1; //error
}
int main() {
printf("1. Value is %f\n", lookup(6.9453));
printf("2. Value is %f\n", lookup(4.666));
printf("3. Value is %f\n", lookup(4.6));
return 0;
}
Yes, you can read them from the dat file. The question is, what format is the dat file? Once you know that, you want to use:
fopen
fread
fclose
for C and
ifstream
for C++ (or something similar).
The program still has to get those pairs from the file and load them in memory. You can loop through the lines in the file, parse the pairs and shove them in a std::map.
Something like this:
#include<fstream>
#include<map>
...
ifstream infile("yourdatfile.dat");
std::string str;
std::map<double, double> m; //use appropriate type(s)
while(getline(infile, str)){
//split str by comma or some delimiter and get the key, value
//put key, value in m
}
//use m
For the signal processing toolbox you can export data to C header files
directly from Matlab(don't know if it's your particular case):
Matlab export to C header
Or maybe the following article could be of help:
Exporting/Importing Data To/From MATLAB
One of options is to generate the C++ lookup table in matlab. Just write to some text file (lookup.cpp), read table producing C++ source...
Related
I have the data in my vector. I am trying to write each vector value, say vector_name[0] into "examplezero.h" , vector_name[1] into "exampleone.h" and so on. The below code shows how I have created the files.
int co = 80;
string name ="example";
std::ofstream output_file[80];
for (int i = 0; i < co; i++)
{
output_file[i].open(name + std::to_string(i) + ".h");
output_file[i].close();
}
I am trying to iterate over my vector and trying to write to my files.
std::vector<string> rowname; //This has all the values
for (auto i = rowname.begin(); i != rowname.end(); ++i)
{
std::ostream_iterator<std::string> \
output_iterator(output_file[80], "\n");
std::copy(rowname.begin(), rowname.end(), output_iterator);
}
When I am trying to write to the files it is crashing. Can you let me know what's wrong? I know the basics of C++ and trying to learn the advanced concepts.
Thanks
Your program is likely crashing because you wrote this code:
std::ostream_iterator<std::string> \
output_iterator(output_file[80], "\n");
...and output_file[80] is one element past the end of the array. You declared it as:
std::ofstream output_file[80];
The first element of that array is output_file[0] and the last element of that array is output_file[79].
There are more things wrong
As #walnut pointed out, if your code is really as you posted it, then it appears to close each file immediately after opening it, without writing anything to the file.
for (int i = 0; i < co; i++)
{
output_file[i].open(name + std::to_string(i) + ".h");
output_file[i].close(); // Leaving so soon?
}
Writing to an ofstream that has been closed does not crash the program, but sets an error condition on the ofstream (badbit). So this will appear to be a silent failure to you.
To fix
To fix your problem you'll have to write to your file after you open it, but before you close it.
You'll also have to decide exactly which output_file you actually want to write to and provide the correct array index. It's not obviously clear from your sample code what your intent was. You'll have to decide which file(s) (of the 80 that you opened) you want to write each element of your rowname vector into.
The std::copy as you have written it will write all strings in the rowname vector to the same stream. If your intent was to write each element to its own file, then you'll have to set it up substantially differently.
Something more along the lines of:
#include <fstream>
#include <vector>
#include <string>
int main() {
std::vector<std::string> rowname = { "alpha", "bravo", "charlie" }; // example data
std::string name = "example"; // base filename
for (size_t i = 0; i < rowname.size(); ++i) {
std::ofstream output_file;
std::string filename = name + std::to_string(i) + ".h"; // e.g.: "example0.h"
output_file.open(filename);
output_file << rowname[i]; // write the string to the file
output_file.close(); // if you want
}
}
This writes the text alpha into example0.h, bravo into example1.h, and charlie into example2.h.
I know how to pass in strings from a text file. In a previous project I read in strings and then tested them on either being "t" or "f", which the result of would set a variable to true or false.
Now I am wondering if it is efficiently possible to read numbers from a text file and pass them into an int? All I can think of is checking for the string "1" and returning 1 in a function, but that would have to be done for every possible integer I could expect in my program, which is not an effective solution.
For context, I am trying to make a save system for a game, and ints/floats that are read in would be variables such as player health, how much of an item they have, etc.
If you already know how to read a string str from a text file, reading numbers is not that difficult: jsut read the string as you did and use stoi() to convert the string into an int, or stof() into float.
int i; double d;
i=stroi(str); d=strod(str2);
Another technique is to use file streams to read or write from a file exactly as you would do from cin and cout:
ifstream file("mytext.txt");
file>>i>>d;
The previous method doesn't care so much about lines. So still another technique is to read a string, convert it into a string stream and use the stringstream as you would with cin:
if (getline(file, str)){ // read a full line
stringstream sst(str);
sst>>i>>d;
}
Using std::fstream. You can open a file, and stream input or output based on how you opened the file.
Example:
#include <iostream>
#include <fstream>
int main(int argc, char** argv)
{
// Pretend we are passed the file location as a command-line argument to our program:
std::fstream file { argv[1], std::ios::in };
if (file.is_open())
{
int value;
file >> value;
std::cout << value << std::endl;
}
else
{
std::cout << "Could not open file " << argv[1] << std::endl;
}
}
Provided that the information is correctly formatted in the file, this should work.
I didn't run it, so there might be syntax errors, but the basics are there. Check out cppreference for some help, they will have further examples.
I'm trying to read specific values (i.e. values#coordinate XY) from a .csv file and struggle with a proper way to define multidimensional arrays within that .csv.
Here's an example of the form from my .csv file
NaN,NaN,1.23,2.34,9.99
1.23,NaN,2.34,3.45,NaN
NaN,NaN,1.23,2.34,9.99
1.23,NaN,2.34,3.45,NaN
1.23,NaN,2.34,3.45,NaN
NaN,NaN,1.23,2.34,9.99
1.23,NaN,2.34,3.45,NaN
NaN,NaN,1.23,2.34,9.99
1.23,NaN,2.34,3.45,NaN
1.23,NaN,2.34,3.45,NaN
NaN,NaN,1.23,2.34,9.99
1.23,NaN,2.34,3.45,NaN
NaN,NaN,1.23,2.34,9.99
1.23,NaN,2.34,3.45,NaN
1.23,NaN,2.34,3.45,NaN
...
Ok, in reality, this file becomes very large. You can interpret rows=latitudes and columns=longitudes and thus each block is an hourly measured coordinate map. The blocks usually have the size of row[361] column[720] and time periods can range up to 20 years (=24*365*20 blocks), just to give you an idea of the data size.
To structure this, I thought of scanning through the .csv and define each block as a vector t, which I can access by choosing the desired timestep t=0,1,2,3...
Then, within this block I would like to go to a specific line (i.e. latitude) and define it as a vector longitudeArray.
The outcome shall be a specified value from coordinate XY at time Z.
As you might guess, my coding experience is rather limited and this is why my actual question might be very simple: How can I arrange my vectors in order to be able to call any random value?
This is my code so far (sadly it is not much, cause I don't know how to continue...)
#include <fstream>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
int longitude, latitude; //Coordinates used to specify desired value
int t; //Each array is associated to a specific time t=0,1,2,3... (corresponds to hourly measured data)
string value;
vector<string> t; //Vector of each block
vector<string> longitudeArray; //Line of array, i.e. latitude
ifstream file("swh.csv"); //Open file
if (!file.is_open()) //Check if file is opened, if not
print "File could..."
{
cout << "File could not open..." << endl;
return 1;
}
while (getline(file, latitude, latitude.empty())) //Scan .csv (vertically) and delimit every time a white line occurs
{
longitudeArray.clear();
stringstream ss(latitude);
while(getline(ss,value,',') //Breaks line into comma delimited fields //Specify line number (i.e. int latitude) here??
{
latitudeArray.push_back(value); //Adds each field to the 1D array //Horizontal vector, i.e. latitude
}
t.push_back(/*BLOCK*/) //Adds each block to a distinct vector t
}
cout << t(longitudeArray[5])[6] << endl; //Output: 5th element of longitudeArray in my 6th block
return 0;
}
If you have any hint, especially if there is a better way handling large .csv files, I'd be very grateful.
Ps: C++ is inevitable for this project...
Tüdelüü,
jtotheakob
As usual you should first think in terms of data and data usage. Here you have floating point values (that can be NaN) that should be accessible as a 3D thing along latitude, longitude and time.
If you can accept simple (integer) indexes, the standard ways in C++ would be raw arrays, std::array and std::vector. The rule of thumb then says: if the sizes are known at compile time arrays (or std::array if you want operation on global arrays) are fine, else go with vectors. And if unsure std:vector is your workhorse.
So you will probably end with a std::vector<std::vector<std::vector<double>>> data, that you would use as data[timeindex][latindex][longindex]. If everything is static you could use a double data[NTIMES][NLATS][NLONGS] that you would access more or less the same way. Beware if the array is large, most compilers will choke if you declare it inside a function (including main), but it could be a global inside one compilation unit (C-ish but still valid in C++).
So read the file line by line, feeding values in your container. If you use statically defined arrays just assign each new value in its position, if you use vectors, you can dynamically add new elements with push_back.
This is too far from your current code for me to show you more than trivial code.
The static (C-ish) version could contain:
#define NTIMES 24*365*20
#define NLATS 361
#define NLONGS 720
double data[NTIMES][NLATS][NLONGS];
...
int time, lat, long;
for(time=0; time<NTIMES; time++) {
for (lat=0; lat<NLATS; lat++) {
for (long=0; long<NLONGS; long++) {
std::cin >> data[time][lat][long];
for (;;) {
if (! std::cin) break;
char c = std::cin.peek();
if (std::isspace(c) || (c == ',')) std::cin.get();
else break;
}
if (! std::cin) break;
}
if (! std::cin) break;
}
if (! std::cin) break;
}
if (time != NTIMES) {
//Not enough values or read error
...
}
A more dynamic version using vectors could be:
int ntimes = 0;
const int nlats=361; // may be a non compile time values
const int nlongs=720; // dito
vector<vector<vector<double>>> data;
int lat, long;
for(;;) {
data.push_back(vector<vector<double>>);
for(lat=0; lat<nlats; lat++) {
data[ntimes].push_back(vector<double>(nlongs));
for(long=0; long<nlongs; long++) {
std::cin >> data[time][lat][long];
for (;;) {
if (! std::cin) break;
char c = std::cin.peek();
if (std::isspace(c) || (c == ',')) std::cin.get();
else break;
}
if (! std::cin) break;
}
if (! std::cin) break;
}
if (! std::cin) break;
if (lat!=nlats || long!=nlongs) {
//Not enough values or read error
...
}
ntimes += 1;
}
This code will successfully process NaN converting it the special not a number value, but it does not check the number of fields per line. To do that, read a line with std::getline and use a strstream to parse it.
Thanks, I tried to transfer both versions to my code, but I couldn't make it run.
Guess my poor coding skills aren't able to see what's obvious to everyone else. Can you name the additional libs I might require?
For std::isspace I do need #include <cctype>, anything else missing which is not mentioned in my code from above?
Can you also explain how if (std::isspace(c) || (c == ',')) std::cin.get(); works? From what I understand, it will check whether c (which is the input field?) is a whitespace, and if so, the right term becomes automatically "true" because of ||? What consequence results from that?
At last, if (! std::cin) break is used to stop the loop after we reached the specified array[time][lat][long]?
Anyhow, thanks for your response. I really appreciate it and I have now an idea how to define my loops.
Again thank you all for your ideas.
Unfortunately, I was not able to run the script... but my task changed slightly, thus the need to read very large arrays is not required anymore.
However, I've got an idea of how to structure such operations and most probably will transfer it to my new task.
You may close this topic now ;)
Cheers
jtothekaob
I've been scratching my head and putting this homework off for a couple days but now that I hunker down to try and do it I'm coming up empty. There's 4 things I need to do.
1) Read a binary file and place that data into arrays
2) Sort the list according to the test scores from lowest to highest
3) Average the scores and output it
4) Create a new binary file with the sorted data
This is what the binary data file looks unsorted
A. Smith 89
T. Phillip 95
S. Long 76
I can probably sort since I think I know how to use parallel arrays and index sorting to figure it out, but the reading of the binary file and placing that data into an array is confusing as hell to me as my book doesn't really explain very well.
So far this is my preliminary code which doesn't really do much:
#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <Windows.h>
using namespace std;
int get_int(int default_value);
int average(int x, int y, int z);
int main()
{
char filename[MAX_PATH + 1];
int n = 0;
char name[3];
int grade[3];
int recsize = sizeof(name) + sizeof(int);
cout << "Enter directory and file name of the binary file you want to open: ";
cin.getline(filename, MAX_PATH);
// Open file for binary write.
fstream fbin(filename, ios::binary | ios::in);
if (!fbin) {
cout << "Could not open " << filename << endl;
system("PAUSE");
return -1;
}
}
Sorry for such a novice question.
edit: Sorry what the data file stated earlier is what it SHOULD look like, the binary file is a .dat that has this in it when opened with notepad:
A.Smith ÌÌÌÌÌÌÌÌÌÌÌY T. Phillip ÌÌÌÌÌÌÌÌ_ S. Long ip ÌÌÌÌÌÌÌÌL J. White p ÌÌÌÌÌÌÌÌd
Reading a file in c++ is simple:
create a stream from file [so that to read from the stream] (you have filestream[input/output], stringstream ... )
ifstream fin; //creates a fileinput stream
fin.open(fname.c_str(),ifstream::binary); // this opens the file in binary mod
void readFile(string fname)
{
ifstream fin;
fin.open(fname.c_str()); //opens that file;
if(!fin)
cout<<"err";
string line;
while(getline(fin,line)) //gets a line from stream and put it in line (string)
{
cout<<line<<endl;
//reading every line
//process for you need.
...
}
fin.close();
}
as you specify, the file is simply a text file, so you can process each line and do whatever you want.
Reading from a binary file may seem confusing, but it is really relatively simple. You have declared your fstream using your file name and set it to binary, which leaves little to do.
Create a pointer to a character array (typically called a buffer, since this data is typically extracted from this array after for other purposes). The size of the array is determined by the length of the file, which you can get by using:
fbin.seekg(0, fbin.end); //Tells fbin to seek to 0 entries from the end of the stream
int binaryLength = fbin.tellg(); //The position of the stream (i.e. its length) is stored in binaryLength
fbin.seekg(0, fbin.beg); //Returns fbin to the beginning of the stream
Then this is used to create a simple character array pointer:
char* buffer = new char[binaryLength];
The data is then read into the buffer:
fbin.read(buffer, binaryLength);
All the binary data that was in the file is now in the buffer. This data can be accessed very simply as in a normal array, and can be used for whatever you please.
The data you have, however, does not at all seem binary. It looks more like a regular text file. Perhaps, unless explicitly stated, you ought to consider a different method for reading your data.
You know, with that low range of sorting index you can avoid actual sorting (with comparing indices and moving data forth and back). All you have to do is to allocate a vector of vector of strings, resize it to 101. Then traverse the data, storing each: "A. Smith" in 89-th element; "T. Phillip" in 95-th; "S. Long" in 76-th and so on.
Then by iterating the vector elements from begin() to end() you would have all the data already sorted.
It's almost linear complexity (almost, because allocation/resizing of subvectors and strings can be costly) easy and transparent.
trying to figure out how to make a little inventory program and I can't for the life figure out why it isn't working.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
struct record
{
int item_id;
string item_type;
int item_price;
int num_stock;
string item_title;
string item_author;
int year_published;
};
void read_all_records(record records[]);
const int max_array = 100;
int main()
{
record records[max_array];
read_all_records(records);
cout << records[2].item_author;
return 0;
}
void read_all_records(record records[])
{
ifstream invfile;
invfile.open("inventory.dat");
int slot = 0;
for (int count = 0; count<max_array; count++);
{
invfile >> records[slot].item_id >> records[slot].item_type >> records[slot].item_price >> records[slot].num_stock >> records[slot].item_title >> records[slot].item_author >> records[slot].year_published;
slot++;
}
invfile.close();
}
I'm testing it by having it print the second item from records author. When I run it, it doesn't show the authors name at all. The .dat file is located in just about every folder where the project is (I forgot which folder it needs to be in) so it's there.
The issue isn't that the file isn't working. It's the array not printing off anything.
my inv file is basically:
123456
book
69.99
16
title
etc
etc
and repeats for different books/cds etc all on one line, all without spaces. Should just next in.
You should check to see that the file is open.
invfile.open("inventory.dat");
if (!invfile.is_open())
throw std::runtime_error("couldn't open inventory file");
You should check to seen that your file reads are working and breaks when you hit the end of file.
invfile >> records[slot].item_id >> records[slot].item_type ...
if (invfile.bad())
throw std::runtime_error("file handling didn't work");
if (invfile.eof())
break;
You probably want to read each record at time, as it isn't clear from this code how the C++ streams are supposed to differentiate between each field.
Usually you'd expect to use std::getline, split the fields on however you delimit them, and then use something like boost::lexical_cast to do the type parsing.
If I were doing this, I think I'd structure it quite a bit differently.
First, I'd overload operator>> for a record:
std::istream &operator>>(std::istream &is, record &r) {
// code about like you had in `read_all_records` to read a single `record`
// but be sure to return the `stream` when you're done reading from it.
}
Then I'd use an std::vector<record> instead of an array -- it's much less prone to errors.
To read the data, I'd use std::istream_iterators, probably supplying them to the constructor for the vector<record>:
std::ifstream invfile("inventory.dat");
std::vector<record> records((std::istream_iterator<record>(invfile)),
std::istream_iterator<record>());
In between those (i.e., after creating the file, but before the vector) is where you'd insert your error handling, roughly on the order of what #Tom Kerr recommended -- checks for is_open(), bad(), eof(), etc., to figure out what (if anything) is going wrong in attempting to open the file.
Add a little check:
if (!invfile.is_open()) {
cout<<"file open failed";
exit(1);
}
So that way, you don't need to copy your input file everywhere like you do now ;-)
You are reading in a specific order, so your input file should have the same order and required number of inputs.
You are printing 3rd element of the struct records. So you should have at least 3 records. I don't see anything wrong with your code. It would a lot easier if you can post your sample input file.