Im very new to programming and I'm currently trying to write a code for binary search of a word in .txt file using vector. The program checks if the word is found if not the searched word is written to the .txt file .The problem is I'm not quite sure I use std::vector correctly and I'm almost sure there is a big problem with my BinarySearch() function.I have read almost every code on the internet for binary_search but I just can't make it work. I can really use some help... The txt file is sorted(one word on each row).The current code finds only 2-3 out of 15 words.Here is my latest attempt:
void BinarySearch(vector<string> cont,string s)
{
int middle;
int first=0;
int leng=cont.size();
int last=leng-1;
bool found=false;
while(first<=last && !found)
{
middle=(first+last)/2;
if(cont[middle]==s)
{
found=true;
}
else {
if(cont[middle]<s)
{
last=middle-1;
}
else
{
first=middle+1;
You were extremely close. But you've got to learn to use the debugger, cause this is a pretty simple catch. This line: if(container[middle]<search) is saying:
Get container's element at middle
Compare it to search
If it comes alphabetically earlier execute the if-block, otherwise execute the else-block
The if-block moves last to search the alphabetically earlier strings, which is the opposite of what you want. This line should have said:
if(container[middle] > search)
Here's a Live example of your code working perfectly after I changed that character: http://ideone.com/vvbONO
Sounds like this is a programming assignment, in which case your teacher probably wouldn't be happy with you solving it like this, but since you have correctly used a sorted vector<string> you can also use: binary_search to completely replace your BinarySearch. Just replace this:
BinarySearch(sWord,find);
With:
cout << (binary_search(cbegin(sWord), cend(sWord), find) ? "word is found" : "Not found") << endl;
If you have questions, comment away!
Related
The problem I'm having is that in the following loop, I'm attempting to read sentences one by one from the input file (inSentences) and output it into another file (outMatch), if it contains a certain word. I am not allowed to use any string functions except for .at() and .size().
The problem lies in that I'm trying to output the sentence first into a intermediary file and then use the extraction operator to get the word one by one to see if it has the word. If it does, it outputs the sentence into the outMatch file. While debugging I found that the sentence variable receives all of the sentences one by one, but the sentMore variable is always extracting out the first sentence of the file, so it's not able to test the rest of the sentences. I can't seem to fix this bug. Help would be greatly appreciated.
P.S. I don't really want the answer fleshed out, just a nudge or a clue in the right direction.
outMatch.open("match");
outTemp.open("temp");
while(getline(inSentences, sentence, '.')){
outTemp << sentence;
outTemp.close();
inTemp.open("temp");
while(inTemp >> sentMore){
if(sentMore == word){
cout << sentence << "." << endl;
inTemp.close();
sentCount++;
}
}
}
You should use string streams! Your issue right now appears to be that you never reopen outTemp, so after the first loop you're trying to write to it after you've closed it. But you can avoid all these problems by switching to stringstreams!
Since you don't want a full solution, an example may look like:
string line_of_text, word;
istringstream strm(line_of_text);
while(strm >> word) {
cout << word << ' ';
}
I am facing a problem with reading and writing a string from and to a file respectively.
Purpose:
To enter a string into a text file as a complete sentence, read the string from the text file and separate all words that start from a vowel using a function and display them as a sentence. (The sentence just needs to consist of the words from the string that start with a vowel.)
Problem:
The code is working as intended but as i have used the getline() function to obtain the string from the txt file when i withdraw a substring from it, it includes the entire file after the vowel instead of just the word. I cannot understand how to make the substring only include words.
Code:
#include <fstream>
#include <string>
#include <iostream>
#include <cstring>
using namespace std;
string vowels(string a)
{
int c=sizeof(a);
string b[c];
string d;
static int n;
for(int i=1;i<=c;i++)
{
if (a.find("a")!=-1)
{
b[i]=a.substr(a.find("a",n));
d+=b[i];
n=a.find("a")+1;
}
else if (a.find("e")!=-1)
{
b[i]=a.substr(a.find("e",n));
d+=b[i];
n=a.find("e")+1;
}
else if (a.find("i")!=-1)
{
b[i]=a.substr(a.find("i",n));
d+=b[i];
n=a.find("i")+1;
}
else if (a.find("o")!=-1)
{
b[i]=a.substr(a.find("o",n));
d+=b[i];
n=a.find("o")+1;
}
else if (a.find("u")!=-1)
{
b[i]=a.substr(a.find("u",n));
d+=b[i];
n=a.find("u")+1;
}
}
return d;
}
int main()
{
string input,lne,e;
ofstream file("output.txt", ios::app);
cout<<"Please input text for text file input: ";
getline(cin,input);
file << input;
file.close();
ifstream myfile("output.txt");
getline(myfile,lne);
e=vowels(lne);
cout<<endl<<"Text inside file reads: ";
cout<<lne;
cout<<endl;
cout<<e<<endl;
system("pause");
myfile.close();
return 0;
}
I haven't read your code VERY carefully, but several things stand out:
Look up find_first_of - it'll simplify your code A LOT.
sizeof(a) certainly doesn't do what you think it does [unless you think it gives you the size of the std::string class type - which makes it rather strange as a use-case, why not use either 12 or 24?]
find (and find_first_of), technically speaking, doesn't return -1 when the function isn't finding what you want. It returns std::string::npos [which may appear to be -1, but a) is not guaranteed to be, and b) is unsingned so can't be negative].
Your program only reads one line.
x.substr(n) will give you the string of x from position n - is that what you want?
Don't repeat find, use p = x.find("X"); and then do x.substr(p) [assuming that is what you want].
There are various problems with your code.
int c = sizeof( a );
This is the number of bytes that a string takes up in memory. And you certainly don't want to create an array of this many strings as it makes no sense for what you're trying to achieve. Don't do this to yourself. You're only copying one string inside the loop, all you need is one string and you already have string d.
To get the actual size of a string, you have to call
str.size()
The string.substr(..) has a couple overloads, one of them takes only one argument, an index. This will return sub string starting at that index in the original string. (The string starting at the vowel all the way through to the end of the string)
What you are maybe looking for is the overload that takes two arguments, the start index (beginning of the word and the end of the word).
The string input will not take the newline that you enter to flush cin. And then you add it to the file in append mode, so after running the program a few times your file is a huge one-liner. Did you really intend to do this?
Maybe you should explicitly add a new line to the file after entering the input. Something like file << std::endl;
Also, the conditions in the ifs
if (a.find("a")!=-1)
Don't match what you do next,
b[i]=a.substr(a.find("a",n));
Then you use a static int,
static int n;
This is bad, because this function will only work once. You're lucky that static initializes its values to zero, but you should always initialize explicitly. In your case, you don't need this to be static.
Finally: "so i was unsure of how many loops to run"
When you don't know how many loops you have to run, then a for loop is not adequate.
You should use a while loop or a do while.
You shouldn't try to learn C++ by guessing, because that's what it looks like you're doing. You're trying to do more than you know and making some very silly mistakes. Find a good book to learn from, or at the very least google the functions you're using to see what they do and how to use them properly. (ie: http://www.cplusplus.com/reference/string/string/substr/ )
Here's a list of books from stackoverflow's FAQ: The Definitive C++ Book Guide and List
The last thing is about finding vowels. When you find a vowel, you have to make sure it's at the beginning of a word. Then you want to read it until the word ends, that is when you find a character that is not part of a word. (a whitespace, certain punctuation, ... ) This should mark the beginning and end of the word.
EDIT: Problem solved! Turns out Windows 7 wont let me read/ write to files without explicitly running as administrator. So if i run as admin it works fine, if i dont i get the weird results i explain below.
I've been trying to get a part of a larger program of mine to read a file.
Despite trying multiple methods(istream::getline, std::getline, using the >> operator etc) All of them return with either /0, blank or a random number/what ever i initialised the var with.
My first thought was that the file didn't exist or couldn't be opened, however the state flags .good, .bad and .eof all indicate no problems and the file im trying to read is certainly in the same directory as the debug .exe and contains data.
I'd most like to use istream::getline to read lines into a char array, however reading lines into a string array is possible too.
My current code looks like this:
void startup::load_settings(char filename[]) //master function for opening a file.
{
int i = 0; //count variable
int num = 0; //var containing all the lines we read.
char line[5];
ifstream settings_file (settings.inf);
if (settings_file.is_open());
{
while (settings_file.good())
{
settings_file.getline(line, 5);
cout << line;
}
}
return;
}
As said above, it compiles but just puts /0 into every element of the char array much like all the other methods i've tried.
Thanks for any help.
Firstly your code is not complete, what is settings.inf ?
Secondly most probably your reading everything fine, but the way you are printing is cumbersome
cout << line; where char line[5]; be sure that the last element of the array is \0.
You can do something like this.
line[4] = '\0' or you can manually print the values of each element in array in a loop.
Also you can try printing the character codes in hex for example. Because the values (character codes) in array might be not from the visible character range of ASCII symbols. You can do it like this for example :
cout << hex << (int)line[i]
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.
I'm having trouble with this algorithm to extract the get variables from a url and print them each on a new line like:
x=y
z=hello
etc. but instead it prints a seemingly random section of the url with no newlines to the file. There must be a logic error of some kind but i just can't spot it.
for(i_m=0;i_m<len_m;i_m++) {
if(var_m[i_m]=='&') {
fwrite(var_m+offset_m, 1, amp_m, echo_out);
fputc('\n',echo_out);
offset_m+=amp_m;
amp_m=0;
}
amp_m++;
}
any help appreciated.
EDIT:
thank you everyone for your comments, I corrected that error Guss but to no avail. I thought up another algorithm, since I can't use c++ strings in this one
while((i_m=(strchr(var_m,'&')-var_m))>0) {
var_m[i_m]='\n';
}
Which would change each of the & to a newline, and then I could just write var_m to the file, but for some reason this gives me a buffer overflow.
void StringExplode(std::string &str, const std::string &separator, std::vector<string>* results){
int found;
found = str.find_first_of(separator);
while(found != string::npos){
if(found > 0){
results->push_back(str.substr(0,found));
}
str = str.substr(found+1);
found = str.find_first_of(separator);
}
if(str.length() > 0){
results->push_back(str);
}
}
your accounting of offset_m and amp_m seems to be wrong. Take for example the simple string "a&b&c" - your code should have outputed from that the text:
a
b
c
but if you trace through the code you will see that when you get to the first & then offset_m=0 and amp_m=1 and you'd print a - which is Ok but when you get to the second & then offset_m=1 and amp_m=2 which would actually print &b and at no point you'd print the last element.
Using a simple string splitting algorithm like mysqlforums suggested is a common way to handle this task, but I believe you should be able to come up with a simple loop algorithm that will get you what you need. think about it again and try to run through the algorithm in your head (or using pen and paper) to try to understand how it works - I'm sure you'll get it!
If you're still having problems, post something here and I'll try to help again.