Here's part my code:
#include <stdio.h>
#include<string>
#include<string.h>
#include<algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main(){
FILE *in=fopen("C.in","r");
//freopen("C.out","w",stdout);
int maxl=0;
int i;
string word;
vector<string> words;
while(!feof(in)){
fscanf(in,"%s ",word.c_str());
int t=strlen(word.c_str());
if(t>maxl){
maxl=t;
words.clear();
words.insert(words.end(),word);
}else if (t==maxl){
words.insert(words.end(),word);
}
}
the problem occurs at
words.insert(words.end,word)
while
word
contains the word from my file, the vector item
words[i]
contains an empty string.
How is this possible?
fscanf(in,"%s ",word.c_str());
That's never going to work. c_str() is a const pointer to the string's current contents, which you mustn't modify. Even if you do subvert const (using a cast or, in this case, a nasty C-style variadic function), writing beyond the end of that memory won't change the length of the string - it will just give undefined behaviour.
Why not use C++ style I/O, reading into a string so that it automatically grows to the correct size?
std::ifstream in(filename);
std::string word;
while (in >> word) {
if (word.size() > maxl) {
maxl = word.size();
words.clear();
words.push_back(word);
} else if (word.size() == maxl) {
words.push_back(word);
}
}
Related
string *parse(string str,int from){
int i=0,n=0,j,k;
i=j=from;
string *data=new string[6];
while(str[i]){
if(str[i]==' '){
for(k=0;k<(i-j-1);k++){
data[n][k]=str[j+k]; << Error takes place here
}
data[n][k]='\0';
j=i;
n++;
}
i++;
}
return data;
}
Thanks for your help. I tried to debug but without success, what am I missing?
The problem is that elements data[i] of the data array all have the length of zero. That is why the assignment data[n][k] is always outside of data[n]'s range.
One way of fixing this would be using concatenation:
data[n] += str[j+k];
A better approach would be eliminating the loop altogether, and using substr member function of std::string instead: it lets you cut out a portion of str knowing the desired length and the starting position.
In addition, you are returning a pointer to a local array, which is undefined behavior. You should replace an array with a vector<string>, and add items to it using push_back.
Finally, you need to push the final word when the str does not end in a space.
Here is your modified program that uses the above suggestions:
vector<string> parse(string str,int from){
int i=from, j=from;
vector<string> data;
while(str[i]){
if(str[i]==' '){
data.push_back(str.substr(j, i-j+1));
j=i+1;
}
i++;
}
if (j != str.size()) {
data.push_back(str.substr(j));
}
return data;
}
Here is a demo on ideone.
data starts with 0 length, data[n][k] out of boundry. data[n][k]='\0' is not correct way of using C++ string and string * is considered of bad practice.
To separate a string by space, try:
#include <string>
#include <vector>
#include <sstream>
std::string data("hi hi hi hi hi");
std::stringstream ss(data);
std::string word;
std::vector<std::string> v;
while(std::getline(ss, word, ' '))
{
v.push_back(word);
}
The following code gives me 2 errors when i compile
#include <iostream>
#include <fstream>
#include <cstring>
#include "Translator.h"
using namespace std;
void Dictionary::translate(char out_s[], const char s[])
{
int i;
char englishWord[MAX_NUM_WORDS][MAX_WORD_LEN];
for (i=0;i < numEntries; i++)
{
if (strcmp(englishWord[i], s)==0)
break;
}
if (i<numEntries)
strcpy(out_s,elvishWord[i]);
}
char Translator::toElvish(const char elvish_line[],const char english_line[])
{
int j=0;
char temp_eng_words[2000][50];
//char temp_elv_words[2000][50]; NOT SURE IF I NEED THIS
std::string str = english_line;
std:: istringstream stm(str);
string word;
while( stm >> word) // read white-space delimited tokens one by one
{
int k=0;
strcpy (temp_eng_words[k],word.c_str());
k++;
}
for (int i=0; i<2000;i++) // ERROR: out_s was not declared in this scope
{
Dictionary::translate (out_s,temp_eng_words[i]); // ERROR RELATES TO THIS LINE
}
}
Translator::Translator(const char dictFileName[]) : dict(dictFileName)
{
char englishWord[2000][50];
char temp_eng_word[50];
char temp_elv_word[50];
char elvishWord[2000][50];
int num_entries;
fstream str;
str.open(dictFileName, ios::in);
int i;
while (!str.fail())
{
for (i=0; i< 2000; i++)
{
str>> temp_eng_word;
str>> temp_elv_word;
strcpy(englishWord[i],temp_eng_word);
strcpy(elvishWord[i],temp_elv_word);
}
num_entries = i;
}
str.close();
}
}
The first one is at std::string istringstream stm(str); where it says it the variable has an initializer but incomplete type. If I put in std::string istringstream stm(str); it says expected initializer before stm andstm was not declared in the scope.
It also says out_s was not declared in this scope at Dictionary::translate (out_s,temp_eng_words[i]);. I don't see why one parameter is recognisied and one is not?
Thanks in advance.
You have to include header file:
#include <sstream>
#include <string>
when you want to use stringstream and string.
Meanwhile:
Dictionary::translate (out_s,temp_eng_words[i]);
If out_s is not a member of the class, you seems forgot to define out_s before using it inside toElvish.
Meanwhile:
while( stm >> word) // read white-space delimited tokens one by one
{
int k=0; //^^Why do you initialize k everytime you read a word?
strcpy (temp_eng_words[k],word.c_str());
k++;
}
You just need to include sstream
Your translator would be much simpler if you used std::map.
#include <map>
#include <string>
// map[english word] returns the elvish word.
typedef std::map<std::string, std::string> Dictionary;
// Define the dictionary
Dictionary english_to_elvish_dictionary;
std::string To_Elvish(const std::string& english_word)
{
Dictionary::iterator iter;
std::string elvish_word;
iter = english_to_elvish_dictionary.find(english_word);
if (iter != english_to_elvish_dictionary.end())
{
// English word is in dictionary, return the elvish equivalent.
elvish_word = *iter;
}
return elvish_word;
}
The above code fragment replaces most of your code and reduces your issues with arrays of arrays of C-strings. Less code == less problems.
To see a list of issues your having, search StackOverflow for "[c++] elvish english".
I am stuck on a homework assignment. I have to read text from a file, allocate each word to memory, then user a pointer to send it to a vector<string*>. My program keeps overwriting the vector with the new word from the file instead of just adding it. I can't figure out why this is happening.
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
using namespace std;
void WordFunctions(string *pstr, vector<string*> &words)
{
words.push_back(pstr);
}
int main(){
ifstream file;
vector<string*> a;
string word;
int w =0;
file.open("word.txt");
while (!file.eof())
{
w++;
file >> word;
WordFunctions(&word, a);
}
file.close();
for (int i=0;i<10;i++){
cout<<(*a[i])<<" ";
delete a[i];
}
system ("pause");
}
Either use a vector<string> or allocate the new string on the heap:
void WordFunctions(string *pstr, vector<string*> &words)
{
words.push_back(new string(*pstr));
}
You are pushing the same element into vector which is the address of word. I massage a bit on your code
// pass reference to eliminate copy
void WordFunctions(string &str, vector<string> &words)
{
words.push_back(str);
}
int main(){
ifstream file;
vector<string> a; // you want to store string not the address of the string
string word;
int w =0;
file.open("words.txt");
while (!file.eof())
{
w++;
word.clear(); // clear the content before store something into it
file >> word;
WordFunctions(word, a);
}
file.close();
for (size_t i=0;i<a.size();i++){ // use size instead of hard code magic number
cout<<(a.at(i))<<" "; // use at function instead of []
}
system ("pause");
}
your word string has always the same address in memory, so in the loop you are changing the value of the string, but then you call WordFunctions passing to him always the same address.
If it's a constraint to use vector<string*> instead of vector<string>, you will likely need to allocate memory for new strings in the loop, copy there your word and then pass the new reference to WordFunctions
char *wordPtr
while (!file.eof())
{
w++;
file >> word;
wordPtr = (char *)malloc((strlen(word)+1)*sizeof(char));
strcpy(wordPtr, *word);
WordFunctions(wordPtr, a);
}
I'm trying to load lines of a text file containing dictionary words into an array object. I want an array to hold all the words that start with "a", another one for "b" ... for all the letters in the alphabet.
Here's the class I wrote for the array object.
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
class ArrayObj
{
private:
string *list;
int size;
public:
~ArrayObj(){ delete list;}
void loadArray(string fileName, string letter)
{
ifstream myFile;
string str = "";
myFile.open(fileName);
size = 0;
while(!myFile.eof())
{
myFile.getline(str, 100);
if (str.at(0) == letter.at(0))
size++;
}
size -= 1;
list = new string[size];
int i = 0;
while(!myFile.eof())
{
myFile.getline(str, 100);
if(str.at(0) == letter.at(0))
{
list[i] = str;
i++;
}
}
myFile.close();
}
};
I'm getting an error saying:
2 IntelliSense: no instance of overloaded function "std::basic_ifstream<_Elem, _Traits>::getline [with _Elem=char, _Traits=std::char_traits<char>]" matches the argument list d:\champlain\spring 2012\algorithms and data structures\weeks 8-10\map2\arrayobj.h 39
I guess it's requiring me to overload the getline function, but I'm not quite certain how to go about or why it's necessary.
Any advice?
the function for streams that deals with std::string is not a member function of istream but rather a free function it is used like so. (the member function version deals with char*).
std::string str;
std::ifstream file("file.dat");
std::getline(file, str);
It is worth noting there are better safer ways to do what you are trying to do like so:
#include <fstream>
#include <string>
#include <vector>
//typedeffing is optional, I would give it a better name
//like vector_str or something more descriptive than ArrayObj
typedef std::vector<std::string> > ArrayObj
ArrayObj load_array(const std::string file_name, char letter)
{
std::ifstream file(file_name);
ArrayObj lines;
std::string str;
while(std::getline(file, str)){
if(str.at(0)==letter){
lines.push_back(str);
}
}
return lines;
}
int main(){
//loads lines from a file
ArrayObj awords=load_array("file.dat", 'a');
ArrayObj bwords=load_array("file.dat", 'b');
//ao.at(0); //access elements
}
don't reinvent the wheel; checkout vectors they are standard and will save you a lot of time and pain.
Final try not to put in using namespace std that is bad for a whole host of reasons I wont go into; instead prefix std objects with std:: so like std::cout or std::string.
http://en.cppreference.com/w/cpp/container/vector
http://en.cppreference.com/w/cpp/string/basic_string/getline
http://en.cppreference.com/w/cpp/string
I have comma delimited strings I need to pull values from. The problem is these strings will never be a fixed size. So I decided to iterate through the groups of commas and read what is in between. In order to do that I made a function that returns every occurrence's position in a sample string.
Is this a smart way to do it? Is this considered bad code?
#include <string>
#include <iostream>
#include <vector>
#include <Windows.h>
using namespace std;
vector<int> findLocation(string sample, char findIt);
int main()
{
string test = "19,,112456.0,a,34656";
char findIt = ',';
vector<int> results = findLocation(test,findIt);
return 0;
}
vector<int> findLocation(string sample, char findIt)
{
vector<int> characterLocations;
for(int i =0; i < sample.size(); i++)
if(sample[i] == findIt)
characterLocations.push_back(sample[i]);
return characterLocations;
}
vector<int> findLocation(string sample, char findIt)
{
vector<int> characterLocations;
for(int i =0; i < sample.size(); i++)
if(sample[i] == findIt)
characterLocations.push_back(sample[i]);
return characterLocations;
}
As currently written, this will simply return a vector containing the int representations of the characters themselves, not their positions, which is what you really want, if I read your question correctly.
Replace this line:
characterLocations.push_back(sample[i]);
with this line:
characterLocations.push_back(i);
And that should give you the vector you want.
If I were reviewing this, I would see this and assume that what you're really trying to do is tokenize a string, and there's already good ways to do that.
Best way I've seen to do this is with boost::tokenizer. It lets you specify how the string is delimited and then gives you a nice iterator interface to iterate through each value.
using namespace boost;
string sample = "Hello,My,Name,Is,Doug";
escaped_list_seperator<char> sep("" /*escape char*/, ","/*seperator*/, "" /*quotes*/)
tokenizer<escaped_list_seperator<char> > myTokens(sample, sep)
//iterate through the contents
for (tokenizer<escaped_list_seperator<char>>::iterator iter = myTokens.begin();
iter != myTokens.end();
++iter)
{
std::cout << *iter << std::endl;
}
Output:
Hello
My
Name
Is
Doug
Edit If you don't want a dependency on boost, you can also use getline with an istringstream as in this answer. To copy somewhat from that answer:
std::string str = "Hello,My,Name,Is,Doug";
std::istringstream stream(str);
std::string tok1;
while (stream)
{
std::getline(stream, tok1, ',');
std::cout << tok1 << std::endl;
}
Output:
Hello
My
Name
Is
Doug
This may not be directly what you're asking but I think it gets at your overall problem you're trying to solve.
Looks good to me too, one comment is with the naming of your variables and types. You call the vector you are going to return characterLocations which is of type int when really you are pushing back the character itself (which is type char) not its location. I am not sure what the greater application is for, but I think it would make more sense to pass back the locations. Or do a more cookie cutter string tokenize.
Well if your purpose is to find the indices of occurrences the following code will be more efficient as in c++ giving objects as parameters causes the objects to be copied which is insecure and also less efficient. Especially returning a vector is the worst possible practice in this case that's why giving it as a argument reference will be much better.
#include <string>
#include <iostream>
#include <vector>
#include <Windows.h>
using namespace std;
vector<int> findLocation(string sample, char findIt);
int main()
{
string test = "19,,112456.0,a,34656";
char findIt = ',';
vector<int> results;
findLocation(test,findIt, results);
return 0;
}
void findLocation(const string& sample, const char findIt, vector<int>& resultList)
{
const int sz = sample.size();
for(int i =0; i < sz; i++)
{
if(sample[i] == findIt)
{
resultList.push_back(i);
}
}
}
How smart it is also depends on what you do with those subtstrings delimited with commas. In some cases it may be better (e.g. faster, with smaller memory requirements) to avoid searching and splitting and just parse and process the string at the same time, possibly using a state machine.