When I try to parse whitespace seperated double values from a string, I found this curious behaviour that the string is read out in a cyclic manner.
Here's the program:
stringstream ss;
string s("1 2 3 4");
double t;
list<double> lis;
for(int j=0; j!=10; ++j){
ss << s;
ss >> t;
lis.push_back(t);
}
for(auto e : lis){
cout << e << " ";
}
Here the output:
1 2 3 41 2 3 41 2 3 41
If I append a trailing space as s= "1 2 3 4 "; I get
1 2 3 4 1 2 3 4 1 2
Now the questions:
1) If I don't know how many entries are in the string s, how do I read all into the list l?
2) which operator<< am I actually calling in ss << s;? Is it specified to read circularly?
3) Can I do the parsing in a better way?
Thanks already!
Here's the fixed code (thanks to timrau):
// declarations as before
ss << s;
while(ss >> t){
lis.push_back(t);
}
// output as before
This produces:
1 2 3 4
as desired. (Don't forget to clear your stringstream by ss.clear() before treating the next input. ;))
Another useful comment from HeywoodFloyd: One could also use boost/tokenizer to "split" the string, see this post
You can test the return value of >>.
while (ss >> t) {
lis.push_back(t);
}
It's not specified to read circularly. It's ss << s appending "1 2 3 4" to the end of the stream.
Before the 1st loop:
""
After 1st ss << s:
"1 2 3 4"
After 1st ss >> t:
" 2 3 4"
After 2nd ss << s:
" 2 3 41 2 3 4"
Then it's clear why you get 1 2 3 41 2 3 41 2 3 41 if there is no trailing space in s.
then use s.length() for strings containing unknown number of entries, if you use your approach.
Or, as suggested by timrau, just initialize your stringstream once.
stringstream ss;
string s("1 2 3 4 5 6 7 8");
ss << s;
double t;
list<double> lis;
while (ss >> t) {
lis.push_back(t);
}
for(auto e : lis){
cout << e << " ";
}
This stackoverflow post includes a boost tokenizer example. You may want to tokenize your string and iterate through it that way. That will solve the no trailing space problem timrau pointed out.
Related
I'm trying to read in this text file:
8 4 4 6 1
8 4 4 6 2
8 4 4 6 3
8 4 4 6 4
8 4 4 6 5
8 4 4 6 6
8 4 4 6 7
8 4 4 6 8
11 4 4 6 3
15 11 13
7 2 1 4 4
9 4 3 9 9
8 2 1 5 4
10 1 2 3 4 6 1
6 1 1 2 5 3 2
13 1 1 2 10 3 8
11 2 11 10 7
And printing it exactly as shown to the console (to make sure I got every input).
However, for some reason my code crashes after reading in the first line. I can't even terminate the debugger.
Here's my code:
while(getline(inFile, buffer)){
buffer2 = strdup(buffer.c_str());
line = strtok(buffer2, " ");
size = atoi(line);
cout << size << " ";
while(line!=NULL){
line = strtok(NULL, " ");
cout << line << " ";
}
cout << "~~~~~~~~~" << endl;
}
If you are going to use C++ you should take advantage of that, use string streams:
#include <fstream>
#include <sstream>
#include <iostream>
using namespace std; //for sample purposes, should not be used
int main() {
int temp, count = 0, sum = 0, total = 0;
string buffer;
ifstream myFile("in.txt");
if (!myFile.is_open())
cout << "No file" << endl;
else{
while(getline(myFile, buffer)){
sum = 0;
stringstream ss(buffer);
while(ss >> temp){
count++; //number count
sum += temp; //line sum
cout << temp << " ";
}
total += sum; //total sum
cout << endl << "count: " << count << endl
<< "sum: " << sum << endl << "total: " << total << endl << endl;
}
myFile.close();
}
cout << "~~~~~~~~~" << endl;
}
You are leaking the memory allocated by strdup(). You need to call free() when you are done using buffer2.
But more importantly, strtok() returns NULL when there are no more tokens to return. But it is undefined behavior to pass a NULL char* pointer to operator<<. Your while loop is doing exactly that when it reaches the end of each line, so anything could happen, including crashing.
Try this instead:
while (getline(inFile, buffer)) {
buffer2 = strdup(buffer.c_str());
if (buffer2 != NULL) {
line = strtok(buffer2, " ");
while (line != NULL) {
size = atoi(line);
cout << size << " ";
line = strtok(NULL, " ");
}
free(buffer2);
}
cout << "~~~~~~~~~" << endl;
}
That being said, why are you using strdup(), strtok(), and atoi() at all? You are writing C++ code, you should C++ semantics instead of C semantics. For example, you can use std::istringstream instead, eg:
while (getline(inFile, buffer)) {
istringstream iss(buffer);
while (iss >> size) {
cout << size << " ";
}
cout << "~~~~~~~~~" << endl;
}
As always, there are many possible solutions. I would like to show an additional one. This is using more modern C++ elements, mainly from the algorithm and iterator library.
So, what will we do?
First we read each line as a std::string in a simple for loop with std::getline. Then we will put the line again in a std::istringstream so that we can take advantage of C++ iterator: std::istream_iterator.
This iterator will iterate over the elements in the string and extract all integers. It is like calling the extractor operator ( >> ) for all elements in the line string.
We use the iterator in the so called range constructor of os a std::vector. This inplace created vector, will be added to the destiantion data. So, as a result, we will get vector of vector of int: A 2-dimensional vector.
For debug purposes, we copy each row of intes to std::cout.
Please note that we do really need only very few and very simple statements to fulfill the task.
Please check.
#include <iostream>
#include <string>
#include <algorithm>
#include <sstream>
#include <vector>
#include <iterator>
std::istringstream sourceFile{R"(8 4 4 6 1
8 4 4 6 2
8 4 4 6 3
8 4 4 6 4
8 4 4 6 5
8 4 4 6 6
8 4 4 6 7
8 4 4 6 8
11 4 4 6 3
15 11 13
7 2 1 4 4
9 4 3 9 9
8 2 1 5 4
10 1 2 3 4 6 1
6 1 1 2 5 3 2
13 1 1 2 10 3 8
11 2 11 10 7)"};
int main()
{
// Here we will store the resulting int values
std::vector<std::vector<int>> data{};
for (std::string line{}; std::getline(sourceFile, line); ) {
// Split the line into integers and add to target array
std::istringstream iss(line);
data.emplace_back(std::vector<int>(std::istream_iterator<int>(iss), {}));
}
// Now all data is in our vector of vector of int
// Show read data on screen
std::for_each(data.begin(), data.end(), [](const std::vector<int>& v){
std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " ")); std::cout << "\n";});
return 0;
}
Please note. I do not have files on SO. So I used a std::istringstream as input stream. You may of course exchange it with any other std::ftream
I have made the following script, that is supposed to read from a file:
char match[] = "match";
int a;
int b;
inp >> lin;
while(!inp.eof()) {
if(!strcmp(lin, match)) {
inp >> a >> b;
cout << a << " " << b <<endl;
}
inp >> lin;
}
inp.close();
return num_atm;
}
It is supposed to read all words, and if a line starts with match, it should then also print the rest of the line.
My input file is this:
match 1 2 //1
match 5 2 //2
nope 3 6 //3
match 5 //4
match 1 4 //5
match 5 9 //6
It will correctly print 1 2, 5 2, and skip 3 6. But then, it will get stuck and keep printing 5 0 and continue printing 5 0 for ever. I get that match is put into b, which is an integer, but I don't get why this is looped. Shouldn't the input read match 4 once, try to read/write 5 and match, and then be done with line 4 and the match from line 5? Then it should next read the number 1 and 4 and then match from number 6.
I would also understand that due to the word not fitting into the integer, it would read match in the fifth line again, but that's not what it does.
It goes back to the match in the fourth line which it already read, and reads it again. Why is this?
When you are reading with >> line enndings are handled the same as spaces: They are just more whitespace that is skipped. That means you see
match 1 2
match 5 2
nope 3 6
match 5
match 1 4
match 5 9
But the program sees
match 1 2 match 5 2 nope 3 6 match 5 match 1 4 match 5 9
Let's fast forward to where things go south
Contents of stream:
nope 3 6 match 5 match 1 4 match 5 9
Processing
inp >> lin; // reads nope stream: 3 6 match 5 match 1 4 match 5 9
if(!strcmp(lin, match)) { // nope != match skip body
}
inp >> lin; // reads 3 stream: 6 match 5 match 1 4 match 5 9
if(!strcmp(lin, match)) { // 3 != match skip body
}
inp >> lin; // reads 6 stream: match 5 match 1 4 match 5 9
if(!strcmp(lin, match)) { // 6 != match skip body
}
inp >> lin; // reads match stream: 5 match 1 4 match 5 9
if(!strcmp(lin, match)) { // match != match Enter body
inp >> a >> b; // reads 5 and fails to parse match into an integer.
// stream: match 1 4 match 5 9
// stream now in failure state
cout << a << " " << b <<endl; // prints 5 and garbage because b was not read
}
inp >> lin; // reads nothing. Stream failed
if(!strcmp(lin, match)) { // match != match Enter body
inp >> a >> b; // reads nothing. Stream failed
// stream: match 1 4 match 5 9
// stream now in failure state
cout << a << " " << b <<endl; // prints g and garbage because b was not read
}
Because nothing is ever read, while(!inp.eof()) is utterly worthless. The end of the file can never be reached. The program will loop forever, probably printing whatever it last read. Successfully read.
Fixing this depends entirely on what you want to do if you have a match line without 2 numbers on it, but a typical framework looks something like
std::string line;
while(std::getline(inp, line) // get a whole line. Exit if line can't be read for any reason.
{
std::istringstream strm(line);
std::string lin;
if(strm >> lin && lin == match) // enters if lin was read and lin == match
// if lin can't be read, it doesn't matter.
// strm is disposable
{
int a;
int b;
if (strm >> a >> b) // enters if both a and b were read
{
cout << a << " " << b <<"\n"; // endl flushes. Very expensive. just use a newline.
}
}
}
Output from this should be something like
1 2
5 2
1 4
5 9
If you want to make some use of match 5... Well it's up to you what you want to put in b if there is no b in the file.
I have a file with this format:
11
1 0
2 8 0
3 8 0
4 5 10 0
5 8 0
6 1 3 0
7 5 0
8 11 0
9 6 0
10 5 7 0
11 0
The first line is the number of lines, so I can make a loop to read the file with the number of lines.
For the other lines, I would like to read the file line by line and store the data until I get a "0" on the line that's why there is a 0 at the end of each line.
The first column is the task name.
The others columns are the constraints name.
I tried to code something but It doesn't seem to work
printf("Constraints :\n");
for (int t = 1; t <= numberofTasks; t++)
{
F >> currentTask;
printf("%c\t", currentTask);
F >> currentConstraint;
while (currentConstraint != '0')
{
printf("%c", currentConstraint);
F >> currentConstraint;
};
printf("\n");
};
The "0" represents the end of the constraints for a task.
I think my code doesn't work properly because the constraint 10 for the task 4 contains a "0" too.
Thanks in advance for your help
Regards
The problem is that you are reading individual characters from the file, not reading whole integers, or even line-by-line. Change your currentTask and currentConstraint variables to int instead of char, and use std::getline() to read lines that you then read integers from.
Try this:
F >> numberofTasks;
F.ignore();
std::cout << "Constraints :" << std::endl;
for (int t = 1; t <= numberofTasks; ++t)
{
std::string line;
if (!std::getline(F, line)) break;
std::istringstream iss(line);
iss >> currentTask;
std::cout << currentTask << "\t";
while ((iss >> currentConstraint) && (currentConstraint != 0))
{
std::cout << currentConstraint << " ";
}
std::cout << std::endl;
}
Live Demo
That being said, the terminating 0 on each line is unnecessary. std::getline() will stop reading when it reaches the end of a line, and operator>> will stop reading when it reaches the end of the stream.
Live Demo
I've got a map containing a word and a set of integers as the value.
I want to output the word left aligned and then the integer values in the set in columns that are lined up. I thought that this would work but it seems to output very badly.
How would I go about adjusting this so that the number columns line up with one another and have a decent amount of spaces in between them?
for (auto cbegin = ident_map.begin(); cbegin != ident_map.end(); cbegin++) {
outFile << left << (*cbegin).first << setw(10);
for (set<int>::iterator setITR = (*cbegin).second.begin(); setITR != (*cbegin).second.end(); setITR++) {
outFile << right << *setITR << setw(4);
}
outFile << endl;
}
I think that this should output correctly but it comes out looking like this:
BinarySearchTree 4
Key 4 27
OrderedPair 1 4 8 14
T 4
erase 27
first 7 13
insert 1 4
key 27
kvpair 1 4
map_iterator 1 3 8 14
mitr 3 7 8 13 14
result 4 6 7 13
result2 8 9 14 15
second 6
t 4
value_type 1
Try Boost.Format
Here is a toy example that is similar in spirit to what you want to do. The %|30t| and %|50t| formatters ensure that your numbers are left-justified at the columns 30 and 50 respectively.
#include <iostream>
#include <boost/format.hpp>
int main(int argc, char *argv[]) {
std::cout << "0 1 2 3 4 5 " << std::endl;
std::cout << "012345678901234567890123456789012345678901234567890123456789" << std::endl;
for (int i = 0; i < 10; i++) {
// Set up the format to have 3 variables with vars 2 and 3 at
// columns 30 and 50 respectively.
boost::format fmt("string %1%: %|30t|%2% %|50t|%3%");
// Append values we want to print
fmt = fmt % i;
for (int j = 0; j < 2; j++) {
fmt = fmt % rand();
}
// Write to std::cout
std::cout << fmt << std::endl;
// Or save as a string...
std::string s = fmt.str();
}
return 0;
}
Which when run, produces:
$ ./a.out
0 1 2 3 4 5
012345678901234567890123456789012345678901234567890123456789
string 0: 16807 282475249
string 1: 1622650073 984943658
string 2: 1144108930 470211272
string 3: 101027544 1457850878
string 4: 1458777923 2007237709
string 5: 823564440 1115438165
string 6: 1784484492 74243042
string 7: 114807987 1137522503
string 8: 1441282327 16531729
string 9: 823378840 143542612
How about try using \t instead of setw(). \t is the tab special character. This will do wonders for your formatting as you can just figure out the number of tabs to your first position for each line, then it is as simple as following what format you would like, works great because tab is a uniform size
I am being given input in the form of:
(8,7,15)
(0,0,1) (0,3,2) (0,6,3)
(1,0,4) (1,1,5)
(2,1,6) (2,2,7) (2,5,8)
(3,0,9) (3,3,10) (3,4,11) (3,5,12)
(4,1,13) (4,4,14)
(7,6,15)
where I have to remember the amount of triples there are. I wrote a quick testing program to try read the input from cin and then split string up to get the numbers out of the input. The program doesn't seem to read all the lines, it stops after (1,1,5) and prints out a random 7 afterwards
I created this quick testing function for one of the functions I am trying to create for my assignment:
int main ()
{
string line;
char * parse;
while (getline(cin, line)) {
char * writable = new char[line.size() + 1];
copy (line.begin(), line.end(), writable);
parse = strtok (writable," (,)");
while (parse != NULL)
{
cout << parse << endl;
parse = strtok (NULL," (,)");
cout << parse << endl;
parse = strtok (NULL," (,)");
cout << parse << endl;
parse = strtok (NULL," (,)");
}
}
return 0;
}
Can someone help me fix my code or give me a working sample?
You can use this simple function:
istream& read3(int& a, int& b, int& c, istream& stream = cin) {
stream.ignore(INT_MAX, '(');
stream >> a;
stream.ignore(INT_MAX, ',');
stream >> b;
stream.ignore(INT_MAX, ',');
stream >> c;
stream.ignore(INT_MAX, ')');
return stream;
}
It expects the stream to start at a (, so it skips any characters and stops after the first ( it sees. It reads in an int into a which is passed by reference (so the outside a is affected by this) and then reads up to and skips the first comma it sees. Wash, rinse, repeat. Then after reading the third int in, it skips the closing ), so it is ready to do it again.
It also returns an istream& which has operator bool overloaded to return false when the stream is at its end, which is what breaks the while loop in the example.
You use it like this:
// don't forget the appropriate headers...
#include <iostream>
#include <sstream>
#include <string>
int a, b, c;
while (read3(a, b, c)) {
cout << a << ' ' << b << ' ' << c << endl;
}
That prints:
8 7 15
0 0 1
0 3 2
0 6 3
1 0 4
1 1 5
2 1 6
2 2 7
2 5 8
3 0 9
3 3 10
3 4 11
3 5 12
4 1 13
4 4 14
7 6 15
When you give it your input.
Because this is an assignment, I leave it to you to add error handling, etc.
I've written a blog 9 days back exactly to parse such inputs:
Playing around with Boost.Spirit - Parsing integer triplets
And you can see the output here for your input : http://ideone.com/qr4DA