I get the syntax for getline(ifstream foo, string bar) function and I know its third parameter which is delimiter, is set to '\n'.
I have a file to read, and it has numbers on first and second column.
The problem is that on the third column, I have to read names of countries which may have contain spaces.
I've checked my code is successfully reading numbers from first two columns for sure, but as my code tries to read the country name , I get a 'Segmentation fault (cord dumped)' error message.
My code looks like this:
string name[50];
double year1[50],year2[50];
fstream ifstr;
ifstr.open("thefile.csv");
for (int i=0; (!(ifstr.eof())) || i < 51; i++) {
ifstr >> year1[i] >> year2[i];
getline(ifstr, name[i]);} // expecting this line to be reading/storing
//anything that comes after 3rd column into string array
The given variable for my assignment is way too long and complicated, so I kind of wrote that up to help readability, but that one line is pretty much the problem.
From the instruction sheet, my professor mentioned
Reading the populations is straightforward, and can be done using the
standard file IO functions we covered in class (i.e., ">>" using an
input stream). However, since the names of some countries contain
spaces, we need to use getline instead of >> for the name field.
Fortunately, the country is the final field so we can use ">>" to read
the populations and then a getline to finish the line.
You will need to input data until the end of file is reached. Recall that getline's return value is false if at end of file, so its
easy to check for this.
I looked up all sources available regarding this topic, but I couldn't find one that solves this so far.
Please advise.
Your loop condition is wrong. You should only loop while both of those values are true. If either one of them becomes false, you should stop. So the || should actually be &&.
You also have an out-of-range problem. The condition i < 51 is wrong. A value of 50 for i will overflow your arrays when you index them. So the correct condition is i < 50.
Finally, eof is not the only condition on a stream that should cause you to stop reading. Just use the bool operator of the stream.
for( int i = 0; ifstr && i < 50; i++ )
Related
I have a problem with my code in C++ and need some help. There are some related questions but I couldn't really understand the answers.
I have a text file ('parameters.dat' in the example below) that I want to read in with my code written in C++. The file includes different types of variables: Boolean, doubles and integers as well as some comments which I want to skip when reading.
My file looks something like that:
150 // this is an integer
4e-1 // this is a double
1.05 // another double
0 // this is a logical (Boolean) variable: 0 is false and 1 is true
A simple version of the code that I use is
int N;
double var_1, var_2;
bool inital;
ifstream read_parameters;
read_parameters.open("parameters.dat");
read_parameters >> N >> var_1 >> var_2 >> initial;
read_parameters.close();
The comments seem to ruin everything and even without them there seem to be some problems with reading the logical variables correctly. The file that I try to read is made by me, so I can substitute the '//' above with something else if necessary. Does anyone have any advice?
Thanks in advance!
Simple, cheesy way:
Read a token then read_parameters.ignore(numeric_limits<streamsize>::max(), '\n') to discard the rest of the line. eg:
read_parameters >> N;
read_parameters.ignore(numeric_limits<streamsize>::max(), '\n');
read_parameters >> var_1;
read_parameters.ignore(numeric_limits<streamsize>::max(), '\n');
...
This doesn't care if a comment exists or not, but requires modification if you have two or more tokens on a line.
Oh, and remember to test the state of the stream after reading. Plugging in "fubar" for one of the doubles will currently ruin things. read_parameters will be in an error state that needs to be cleared before you can read it again.
if (!read_parameters >> N)
{
std::cerr << "bad input for parameter N" << std::endl;
read_parameters.clear();
}
read_parameters.ignore(numeric_limits<streamsize>::max(), '\n');
Is better, but you probably want to handle an error with something better than a printline.
Take input in a Dynamic Character array then run a for loop in which if a character has ascii 65 - 97 - onward then it will be Alphabet and else if ascii represents integers like 1,2,3 then separte them in another array after calculating total integers as count++ .
I tried to solve this problem in UVa but I am getting a wrong answer and I cant seem to find the error
http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2525
#include<cstdio>
#include<cstring>
using namespace std;
int main()
{
int t,j,k,i=1;
char a[1000];
while(scanf("%d",&t)!=EOF && t)
{
int sum=0;
getchar();
gets(a);
k=strlen(a);
for(j=0;j<k;j++)
{ if(a[j]=='a'||a[j]=='d'||a[j]=='g'||a[j]=='j'||a[j]=='m'||a[j]=='p'||a[j]=='t'||a[j]=='w'||a[j]==32)
sum=sum+1;
else if(a[j]=='b'||a[j]=='e'||a[j]=='h'||a[j]=='k'||a[j]=='n'||a[j]=='q'||a[j]=='u'||a[j]=='x')
sum=sum+2;
else if(a[j]=='c'||a[j]=='f'||a[j]=='i'||a[j]=='l'||a[j]=='o'||a[j]=='r'||a[j]=='v'||a[j]=='y')
sum=sum+3;
else if(a[j]=='s'||a[j]=='z')
sum=sum+4;
}
printf("Case #%d: %d\n",i,sum);
i++;
}
return 0;
}
In the problem description there is a single number that indicates the number of texts that will be in the input afterwards. Your original code was trying to read the number before every row of input.
The attempt to read the number in each one of the rows will fail since the input character set does not include any digits, so you could be inclined to think that there should be no difference. But there is, when you try to read a number it will start by consuming the leading whitespace. If the input is:
< space >< space >a
The output should be 3 (two '0' and one '2' keys), but the attempt to read the number out of the line will consume the two leading whitespace characters and the later gets will read the string "a", rather than " a". Your count will be off by the amount of leading whitespace.
separate your code into functions that do specific things: read the data from the file, calculate the number of key presses for each input, output the result
Benefit:
You can test each function independently. It is also easier to reason about the code.
The maximum size of an input is 100, this means you only need an array of 101 characters( including the final \0) for each input, not 1000.
Since this question is also tagged C++ try to use std::vector and std::string in your code.
The inner for seems right at a cursory glance. The befit of having a specialized function that computes the number of key presses is that you can easily verify it does the correct thing. Make sure you check it thoroughly.
I just need a little help with file parsing. We have to parse a file that has 6 string entries per row in the format:
"string1", "string2", "string3", "string4", "string5", "string6"
My instructor recently gave us a little piece of code as a "hint," and I'm supposed to use it. Unfortunately, I can't figure out how to get it to work. Here's my file parsing function.
void parseData(ifstream &myFile, Book bookPtr[])
{
string bookInfo;
int start, end;
string bookData[6];
getline(myFile, bookInfo);
start = -2;
myFile.open("Book List.txt");
for (int j = 0; j < 6; j++)
{
start += 3;
end = bookInfo.find('"', start);
bookData[j] = bookInfo.substr(start, end-start);
start = end;
}
}
So I'm trying to read the 6 strings into an array of strings. Can someone please help walk me through the process?
start = -2;
for (int j = 0; j < 6; j++)
{
start += 3;
end = bookInfo.find('"', start);
bookData[j] = bookInfo.substr(start, end-start);
start = end;
}
So ", " is four characters. The leading closing quote is 3 characters behind the opening closing quote.
At entry to the loop start is pointing to the last closing quote. (On first entry to loop it is faked as -2 to be pointing to the closing quote of the imaginary "-1th" element.)
So we advance from the last closing quote to the following opening quote:
start += 3;
Then we use std::string::find to find the closing quote:
end = bookInfo.find('"', start);
The offset tells it to ignore all characters up to and including that position.
We then have the two quote positions, start..end, so we use substr to extract the string:
bookData[j] = bookInfo.substr(start, end-start);
And we then update start for the next loop to be the last closing quote:
start = end
Please, for your own sake, create a minimal example. This starts with a string like the line you gave as example and ends with the different parts in an array. Leave the loading from a file out for now, getline() seems to work for you, or? Then, do not declare every variable you might want to use at the beginning of a function. This is not ancient C, where you simply had to do that or introduce additional {} blocks. There is another thing odd, and that is the Book bookPtr[]. This is indeed just a Book* bookPtr, i.e. you are not passing an array to a function but just a pointer. Don't fall for this misleading syntax, it's a lie! Anyway, you don't seem to be using that pointer to the object(s) of the unknown type anyway.
Concerning the splitting of a line into strings, one approach is to locate pairs of double quotes. Everything in between is one of the strings, everything without is irrelevant. The string class has a find() function which optionally takes a starting position. Starting position is always one behind the previously found position.
Your code above seems to assume that there is exactly one double quote, a comma, a space and another double quote that separates two strings. This isn't 100% clear, I would also be prepared for handling multiple spaces or no space at all. Also, is the comma guaranteed? Are the double quotes guaranteed? Anyway, keep it simple. Unless you get a better spec on the input, just assume that only the parts between the quotes is what differs.
Then, what exactly works and what doesn't? You need to ask more specific questions and give more detailed information. The code above doesn't look broken per se, although there are a few things a bit off. For example, you don't typically pass ifstreams to a function, but use the istream baseclass. In your case, you read a line from that file and then open another file using the same fstream object, which doesn't make sense to me, since you don't use it after that. If you only needed that stream locally, you would create and open it there (handling errors of course!) and pass in the filename as parameter only.
UPDATE: Yes, answered and solved. I also then managed to find the issue with the output that was the real problem I was having. I had thought the substring error was behind it, but I was wrong, as when that had been fixed, the output issue persisted. I found that it was a simple mix up in the calculations. I had been subtracting 726 instead of 762. I could've had this done hours ago... Lulz. That's all I can say... Lulz.
I am teaching myself C++ (with the tutorial from their website). I have jumped ahead time to time when I have needed to do something I cannot with what I have learned so far. Additionally, I wrote this relatively quickly. So, if my code looks inelegant or otherwise unacceptable at a professional level, please do excuse that for now. My only current purpose is to get this question answered.
This program takes each line of a text file I have. Note that the text file's lines look like this:
.123.456.789
It has 366 lines. The program I first wrote to deal with this had me input each of the three numbers for each line manually. As I'm sure you can imagine, that was extremely inefficient. This program's purpose is to take each number out of the text file and perform functions and output the results to another text file. It does this per line until it reaches the end of the file.
I have read up more on what could cause this error, but I cannot find the cause of it in my case. Here is the bit of the code that I believe to contain the cause of the problem:
int main()
{
double a;
double b;
double c;
double d;
double e;
string search; //The string for lines fetched from the text file
string conversion;
string searcha; //Characters 1-3 of search are inserted to this string.
string searchb; //Characters 5-7 of search are inserted to this string.
string searchc; //Characters 9-11 of search are inserted to this string.
string subsearch; //Used with the substring to fetch individual characters.
string empty;
fstream convfil;
convfil.open("/home/user/Documents/MPrograms/filename.txt", ios::in);
if (convfil.is_open())
{
while (convfil.good())
{
getline(convfil,search); //Fetch line from text file
searcha = empty;
searchb = empty;
searchc = empty;
/*From here to the end seems to be the problem.
I provided code from the beginning of the program
to make sure that if I were erring earlier in the code,
someone would be able to catch that.*/
for (int i=1; i<4; ++i)
{
subsearch = search.substr(i,1);
searcha.insert(searcha.length(),subsearch);
a = atof(searcha.c_str());
}
for (int i=5; i<8; ++i)
{
subsearch = search.substr(i,1);
searchb.insert(searchb.length(),subsearch);
b = atof(searchb.c_str());
}
for (int i=9; i<search.length(); ++i)
{
subsearch = search.substr(i,1);
searchc.insert(searchc.length(),subsearch);
c = atof(searchc.c_str());
}
I usually teach myself how to get around these issues when they come up by looking at references and problems other people may have had, but I couldn't find anything that helped me in this instance. I have tried numerous variations upon this, but as the issue has something to do with the substring and I couldn't get rid of the substring in any of these variations, all returned the same error and the same result in the output file.
This is a problem:
while (convfil.good()) {
getline(convfil,search); //Fetch line from text file
You test for failure before you do the operation that can fail. When getline does fail, you're already inside the loop.
As a result, your code tries to process an invalid record at the end.
Instead try
while (getline(convfil,search)) { //Fetch line from text file
or even
while (getline(convfil,search) && search.length() > 9) {
which will also stop without error if there's a blank line at the end of the file.
It's possible you are reading a blank line at the end of the file and trying to process it.
Test for an empty string before processing it.
Ok, just to be up front, this IS homework, but it isn't due for another week, and I'm not entirely sure the final details of the assignment. Long story short, without knowing what concepts he'll introduce in class, I decided to take a crack at the assignment, but I've run into a problem. Part of what I need to do for the homework is read individual characters from an input file, and then, given the character's position within its containing word, repeat the character across the screen. The problem I'm having is, the words in the text file are single words, each on a different line in the file. Since I'm not sure we'll get to use <string> for this assignment, I was wondering if there is any way to identify the end of the line without using <string>.
Right now, I'm using a simple ifstream fin; to pull the chars out. I just can't figure out how to get it to recognize the end of one word and the beginning of another. For the sake of including code, the following is all that I've got so far. I was hoping it would display some sort of endl character, but it just prints all the words out run together style.
ifstream fin;
char charIn;
fin.open("Animals.dat");
fin >> charIn;
while(!fin.eof()){
cout << charIn;
fin >> charIn;
}
A few things I forgot to include originally:
I must process each character as it is input (my loop to print it out needs to run before I read in the next char and increase my counter). Also, the length of the words in 'Animals.dat' vary which keeps me from being able to just set a number of iterations. We also haven't covered fin.get() or .getline() so those are off limits as well.
Honestly, I can't imagine this is impossible, but given the restraints, if it is, I'm not too upset. I mostly thought it was a fun problem to sit on for a while.
Why not use an array of chars? You can try it as follow:
#define MAX_WORD_NUM 20
#define MAX_STR_LEN 40 //I think 40 is big enough to hold one word.
char words[MAX_WROD_NUM][MAX_STR_LEN];
Then you can input a word to the words.
cin >> words[i];
The >> operator ignores whitespace, so you'll never get the newline character. You can use c-strings (arrays of characters) even if the <string> class is not allowed:
ifstream fin;
char animal[64];
fin.open("Animals.dat");
while(fin >> animal) {
cout << animal << endl;
}
When reading characters from a c-string (which is what animal is above), the last character is always 0, sometimes represented '\0' or NULL. This is what you check for when iterating over characters in a word. For example:
c = animal[0];
for(int i = 1; c != 0 && i < 64; i++)
{
// do something with c
c = animal[i];
}