I want to read in lines from a text file into a 2-d char array but without the newline character.
Example of .txt:
TCAGC
GTAGA
AGCAG
ATGTC
ATGCA
ACAGA
CTCGA
GCGAC
CGAGC
GCTAG
...
So far, I have:
ifstream infile;
infile.open("../barcode information.txt");
string samp;
getline(infile,samp,',');
BARCLGTH = samp.length();
NUMSUBJ=1;
while(!infile.eof())
{
getline(infile,samp,',');
NUMSUBJ++;
}
infile.close(); //I read the file the first time to determine how many sequences
//there are in total and the length of each sequence to determine
//the dimensions of my array. Not sure if there is a better way?
ifstream file2;
file2.open("../barcode information.txt");
char store[NUMSUBJ][BARCLGTH+1];
for(int i=0;i<NUMSUBJ;i++)
{
for(int j=0;j<BARCLGTH+1;j++)
{
store[i][j] = file2.get();
}
}
However, I do not know how to ignore the newline character. I want the array to be indexed so that I can access a sequence with the first index and then a specific char within that sequence with the second index; i.e. store[0][0] would give me 'T', but I do not want store[0][5] to give me '\n'.
Also, as an aside, store[0][6], which I think should be out of bounds since BARCLGTH is 5, returns 'G',store[0][7] returns 'T',store[0][8] returns 'A', etc. These are the chars from the next line. Alternatively, store[1][0],store[1][1], and store[1][2] also return the same values. Why does the first set return values, shouldn't they be out of bounds?
As you're coding in C++, you could do like this instead:
std::vector<std::string> barcodes;
std::ifstream infile("../barcode information.txt");
std::string line;
while (std::getline(infile, line))
barcodes.push_back(line);
infile.close();
After this the vector barcodes contains all the contents from the file. No need for arrays, and no need to count the number of lines.
And as both vectors and strings can be indexed like arrays, you can use syntax such as barcodes[2][0] to get the first character of the third entry.
Related
First of all, I didn't code in C++ for more then 8 years, but there is a hobby project I would like to work on where I ran into this issue.
I checked a similar question: Only printing last line of txt file when reading into struct array in C
but in my case I don't have a semicolon at the end of the while cycle.
Anyway, so I have a nicknames.txt file where I store nicknames, one in each line.
Then I want to read these nicknames into an array and select one random element of it.
Example nicknames.txt:
alpha
beta
random nickname
...
Pirate Scrub
Then I read the TXT file:
int nicknameCount = 0;
char *nicknames[2000];
std::string line;
std::ifstream file("nicknames.txt");
FILE *fileID = fopen("asd.txt", "w");
while (std::getline(file, line))
{
nicknames[nicknameCount++] = line.data();
// (1)
fprintf(fileID, "%i: %s\n", nicknameCount - 1, nicknames[nicknameCount - 1]);
}
int randomNickIndex = rand() % nicknameCount;
// (2)
for (int i = 0; i < nicknameCount; i++)
fprintf(fileID, "%i: %s\n", i, nicknames[i]);
fprintf(fileID, "Result: %s\n", nicknames[randomNickIndex]);
fprintf(fileID, "Result: %i\n", randomNickIndex);
fclose(fileID);
exit(0);
What then I see at point (1) is what I expect; the nicknames. Then later at point (2) every single member of the array is "Pirate Scrub", which is the last element of the nicknames.txt.
I think it must be something obvious, but I just can't figure it out. Any ideas?
line.data() returns a pointer to the sequence of characters. It is always the same pointer. Every time you read a new line, the contents of line are overwritten. To fix this, you will need to copy the contents of line.
Change:
char *nicknames[2000];
to
char nicknames[2000][256];
and
nicknames[nicknameCount++] = line.data();
to
strcpy(nicknames[nicknameCount++], line.data());
However, using a vector to store the lines is probably better, since this is C++
Your nicknames array does not contain copies of the strings, all the nicknames are pointers to the same data owned by line.
Instead of char* nicknames[2000] i would recommend you use
std::vector<std::string> nicknames;
and then inside the loop:
nicknames.push_back(line);
This:
char *nicknames[2000];
is an array of 2000 pointers to char. Nowhere in your code you are actually storing the strings from the file. This
nicknames[nicknameCount++] = line.data();
merely stores pointers to the lines internal buffer in the array. In the next iteration this buffer is overwritten with contents of the next line.
Forget about all the C i/o. Mixing C and C++ is advanced and you don't need it here. If you want to store a dynamically sized array of strings in C++, that is a std::vector<std::string>:
std::vector<std::string> lines;
std::string line;
while (std::getline(file, line))
{
lines.push_back(line);
}
Also for writing to the output file you should use an std::ofstream.
I want to read in a line from a text file, store the line in an array of strings to later display the line numbers a word can be found on, and also break down the line into words for marking how many times unique words come up. I have successfully been able to break down the lines word by word and mark the frequency in which they appear but I'm struggling with storing the line in an array of strings so that I can use it later.
void get_word(istream& in_stream, string& w,
list<string> &wordlist, int& lineCount, string *line)
{
string t;
getline(in_stream,t);
for (int j=0; t[j]; j++)
t[j] = tolower(t[j]);
line = &t;
istringstream iss(t);
string word;
while(iss >> word)
{
insert_word(word, wordlist);
}
}
So far this is what I have and no matter what I try to do with the line where I try to assign the string "t" to the "line" array that's being pointed to it doesn't put anything in the array, I think I'm just completely missing something.
line is initialized as:
string line[0];
First of all, string line[0] gives you an array of no strings. That's not likely to be what you intended. Why not simply string line? That's one string. You'd pass a pointer to that string into your function, with &line.
Secondly, line = &t replaces the input pointer with a pointer to the local variable. This information is lost once the function ends. If you write *line = t then you are instead setting "the string that line points to" to the value of "the string t".
Ideally you'd avoid the "out argument" and just return the string you want, though.
string numbers;
string fileName = "text.txt";
ifstream inputFile;
inputFile.open(fileName.c_str(),ios_base::in);
inputFile >> numbers;
inputFile.close();
cout << numbers;
And my text.txt file is:
1 2 3 4 5
basically a set of integers separated by tabs.
The problem is the program only reads the first integer in the text.txt file and ignores the rest for some reason. If I remove the tabs between the integers it works fine, but with tabs between them, it won't work. What causes this? As far as I know it should ignore any white space characters or am I mistaken? If so is there a better way to get each of these numbers from the text file?
When reading formatted strings the input operator starts with ignoring leading whitespace. Then it reads non-whitespace characters up to the first space and stops. The non-whitespace characters get stored in the std::string. If there are only whitespace characters before the stream reaches end of file (or some error for that matter), reading fails. Thus, your program reads one "word" (in this case a number) and stops reading.
Unfortunately, you only said what you are doing and what the problems are with your approach (where you problem description failed to cover the case where reading the input fails in the first place). Here are a few things you might want to try:
If you want to read multiple words, you can do so, e.g., by reading all words:
std::vector<std::string> words;
std::copy(std::istream_iterator<std::string>(inputFile),
std::istream_iterator<std::string>(),
std::back_inserter(words));
This will read all words from inputFile and store them as a sequence of std::strings in the vector words. Since you file contains numbers you might want to replace std::string by int to read numbers in a readily accessible form.
If you want to read a line rather than a word you can use std::getline() instead:
if (std::getline(inputFile, line)) { ... }
If you want to read multiple lines, you'd put this operation into a loop: There is, unfortunately, no read-made approach to read a sequence of lines as there is for words.
If you want to read the entire file, not just the first line, into a file, you can also use std::getline() but you'd need to know about one character value which doesn't occur in your file, e.g., the null value:
if (std::getline(inputFile, text, char()) { ... }
This approach considers a "line" a sequence of characters up to a null character. You can use any other character value as well. If you can't be sure about the character values, you can read an entire file using std::string's constructor taking iterators:
std::string text((std::istreambuf_iterator<char>(inputFile)),
std::istreambuf_iterator<char>());
Note, that the extra pair of parenthesis around the first parameter is, unfortunately, necessary (if you are using C++ 2011 you can avoid them by using braces, instead of parenthesis).
Use getline to do the reading.
string numbers;
if (inputFile.is_open())//checking if open
{
getline (inputFile,numbers); //fetches entire line into string numbers
inputFile.close();
}
Your program does behave exactly as in your description : inputFile >> numbers; just extract the first integer in the input file, so if you suppress the tab, inputFile>> will extract the number 12345, not 5 five numbers [1,2,3,4,5].
a better method :
vector< int > numbers;
string fileName = "text.txt";
ifstream inputFile;
inputFile.open(fileName.c_str(),ios_base::in);
char c;
while (inputFile.good()) // loop while extraction from file is possible
{
c = inputFile.get(); // get character from file
if ( inputFile.good() and c!= '\t' and c!=' ' ) // not sure of tab and space encoding in C++
{
numbers.push_back( (int) c);
}
}
inputFile.close();
I'm trying to store strings that I read from a file in a std::vector but I'm getting a weird error...
So I have the container:
std::vector<std::string> m_Strings;
Then I read the string from a stream:
ifstream inStream;
char word[100];
//[...]
inStream >> word;
m_Strings.push_back(word);
Even though the vector is empty, when I insert the first string the vector resizes to hold 8 strings, the string at index 0 containing random characters, at index 1 containing the correct word, and the other indices containing invalid pointers...
Any idea of what might cause this?
EDIT: In this case I'm reading the string "DIRECTIONAL_LIGHT" so it fits in the char word[100]
Just changed char word[100]; to std::string word; and the error disappeared.
What I've been trying to do, is read a line from stdin and split it, by using whitespace as seperators.
Let's say I have this as input:
2
1 2
3 4
The first line gives me the amount of lines I'd like to read, they're all lines with integers seperated by an unknown amount of whitespace (i.e. could be 1 space, but it could also be 10 spaces).
The thing I've been trying to do is reading those lines into dynamically sized arrays of integers.
This was extremely easy in Python:
foo = raw_input()
array = foo.split()
or even shorter:
foo = raw_input().split()
However, because of the circumstances, I have to learn the beauty of C++.
So I tried to create something akin to the above Python code:
#include <iostream>
using namespace std;
int lines;
int *array;
int main() {
cin >> lines;
for (int line = 0; line < lines; line++) {
// Something.
}
}
I don't seem to know a way to split the line of input. I know that std::cin reads until it reaches a whitespace. However, I can't seem to think of something to count the amount of numbers on the line...
A little nudge into the right direction would be appreciated, thanks.
so given all you wanted is a nudge, here are a couple of hints..
std::getline() - allows you to read from a stream into a std::string.
You can then construct a std::istringstream using this string which you've just read in. Then use this stream to read your ints
for example:
std::string line;
if(std::getline(std::cin, line))
{
std::istringstream str(line);
int lc;
if (str >> lc) // now you have the line count..
{
// now use the same technique above
}
}
oh and for your "dynamically sized array", you need to look at std::vector<>
In C++ you can access characters in a string with [], just as if that string were an array. I suggest you read a line from cin into a string, iterate over the string with a for loop and check each character to see whether it is whitespace. Whenever you find a non-whitespace character, store it in your array.