I am trying to compare a string in a vector to another string:
I tried:
vector<string> x;
string y;
if(x[i] == y)
if(x[i].compare(y) == 0)
if(y.compare(x[i]) == 0)
if(x.at(i) == y)
if(x.at(i).compare(y) == 0)
if(y.compare(x.at(i)) == 0)
tried passing x[i] / x.at(i) to string z first, nothing. I get no compile errors, no problems, it just seems the vector at index i does not want to compare?
g++ -v 4.9.3
Windows 7: cygwin64
c++11, compiling using the -std=c++11 call
I print both strings out, they are identical, but it does not want to compare them.
------- source cpp
#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
vector<string> get_file(const char* file){
int SIZE=256, ln=0;
char str[SIZE];
vector<string> strs;
ifstream in(file, ios::in);
if(!in){
return strs;
} else {
while(in.getline(str,SIZE)){
strs.push_back(string(str));
ln++;
}
}
in.close();
return strs;
}
void convert_file(const char* file){
vector<string> s = get_file(file);
vector<string> d;
int a, b;
bool t = false;
for(int i=0; i<s.size(); i++){
string comp = "--";
string m = s.at(i);
cout << m << endl;
if(m == comp){ //test string compare
cout << "s[i] == '--'" << endl;
}
}
}
int main(){
convert_file("dvds.txt");
return 0;
}
----- dvds.txt
--
title:The Shawshank Redemption
director:Stephan King
release_date:14-10-1994
actors:Tim Robbins,Morgan Freeman,Bob Guton
genres:Crime,Drama
rating:R
price:4.99
--
title:Test title
director:Stephan King
release_date:10-10-1990
actors:Morgan Freeman,random 2,random 4
genres:Adventure,Comedy
rating:PG-13
price:4.99
--
title:Test 3
director:None
release_date:15-52-516
actors:Tim Robbins,None,None 2
genres:Crime,Comedy
rating:PG-17
price:4.99
--
---- running
C:\drew\projects>g++ -o a -std=c++11 source.cpp
C:\drew\projects>a
prints out the dvds.txt just fine, but no comparison is being done when it should
Try the following:
#include <string>
#include <iostream>
#include <vector>
int main() {
std::vector<std::string> x;
std::string y("AAAA");
x.push_back("AAAA");
int i = 0;
if (x[i] == y) {
std::cout << y << std::endl;
}
return 0;
}
It works for me. You might want to double check your variables and their types. You might also want to try the same thing with a different compiler.
Related
I am a beginner at coding, and was trying this question that replaces all repetitions of a letter in a string with a hyphen: i.e ABCDAKEA will become ABCD-KE-.I used the switch loop and it works, but i want to make it shorter and maybe use recursion to make it more effective. Any ideas?
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
char x[100];
int count[26]={0}; //initialised to zero
cout<<"Enter string: ";
cin>>x;
for(int i=0; i<strlen(x); i++)
{
switch(x[i])
{
case 'a':
{
if((count[0]++)>1)
x[i]='-';
}
case 'b':
{
if((count[1]++)>1)
x[i]='-';
}
case 'c':
{
if((count[2]++)>1)
x[i]='-';
}
//....and so on for all alphabets, ik not the cutest//
}
}
Iterate through the array skipping whitespace, and put characters you've never encountered before in std::set, if you find them again you put them in a duplicates std::set if you'd like to keep track of how many duplicates there are, otherwise change the value of the original string at that location to a hyphen.
#include <iostream>
#include <string>
#include <cctype>
#include <set>
int main() {
std::string s("Hello world");
std::set<char> characters;
std::set<char> duplicates;
for (std::string::size_type pos = 0; pos < s.size(); pos++) {
char c = s[pos];
// std::isspace() accepts an int, so cast c to an int
if (!std::isspace(static_cast<int>(c))) {
if (characters.count(c) == 0) {
characters.insert(c);
} else {
duplicates.insert(c);
s[pos] = '-';
}
}
}
return 0;
}
Naive (inefficient) but simple approach, requires at least C++11.
#include <algorithm>
#include <cctype>
#include <iostream>
#include <string>
std::string f(std::string s)
{
auto first{s.begin()};
const auto last{s.end()};
while (first != last)
{
auto next{first + 1};
if (std::isalpha(static_cast<unsigned char>(*first)))
std::replace(next, last, *first, '-');
first = next;
}
return s;
}
int main()
{
const std::string input{"ABCDBEFKAJHLB"};
std::cout << f(input) << '\n';
return 0;
}
First, notice English capital letters in ASCII table fall in this range 65-90. Casting a capital letter static_cast<int>('A') will yield an integer. If after casing the number is between 65-90, we know it is a capital letter. For small letters, the range is 97-122. Otherwise the character is not a letter basically.
Check create an array or a vector of bool and track the repetitive letters. Simple approach is
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string str("ABCDAKEAK");
vector<bool> vec(26,false);
for(int i(0); i < str.size(); ++i){
if( !vec[static_cast<int>(str[i]) - 65] ){
cout << str[i];
vec[static_cast<int>(str[i]) - 65] = true;
}else{
cout << "-";
}
}
cout << endl;
return 0;
}
Note: I assume the input solely letters and they are capital. The idea is centered around tracking via bool.
When you assume input charactor encode is UTF-8, you can refactor like below:
#include <iostream>
#include <string>
#include <optional>
#include <utility>
std::optional<std::size_t> char_to_index(char u8char){
if (u8'a' <= u8char && u8char <= u8'z'){
return u8char - u8'a';
}
else if (u8'A' <= u8char && u8char <= u8'A'){
return u8char - u8'A';
}
else {
return std::nullopt;
}
}
std::string repalce_mutiple_occurence(std::string u8input, char u8char)
{
bool already_found[26] = {};
for(char& c : u8input){
if (const auto index = char_to_index(c); index && std::exchange(already_found[*index], true)){
c = u8char;
}
}
return u8input;
}
int main(){
std::string input;
std::getline(std::cin, input);
std::cout << repalce_mutiple_occurence(input, u8'-');
}
https://wandbox.org/permlink/UnVJHWH9UwlgT7KB
note: On C++20, you should use char8_t instead of using char.
I am reading a file using fstream and getline functions. I want to give a starting position e.g. my file has 13 lines I want to start reading it from 7th line for example. Here is my code:
#include<iostream>
#include <stdlib.h>
#include <string>
#include <vector>
#include<iterator> // for iterators
#include<map>
using namespace std;
int main()
{
string line;
int start= 7;
unsigned long int index;
For( int z=1; z<=13; z++){
if (f_node.is_open())
{
getline(f_node, line);
if ((line.find("$EndNodes") != string::npos))
{
cout << "$EndNodes found file closed .... " << endl;
f_node.close();
return false;
}
// Point index.
int i = 0;
int j = line.find_first_of(" ", i);
index = strtoul((line.substr(i, j)).c_str(), NULL, 0);//
}
}
I am reading only indexes and I want to start it from 7th index How to do it?
To discard some number of lines, something like:
#include <fstream>
#include <string>
int main() {
std::ifstream infile{"myfile.txt"};
std::string line;
int starting_line = 7;
// Read and discard beginning lines
for (int n = 1; n < starting_line; n += 1) {
if (!std::getline(infile, line)) {
// Error or premature end of file! Handle appropriately.
}
}
while (std::getline(infile, line)) {
// Do something with the lines you care about.
}
return 0;
}
Except with actual error checking and handling and such.
"there is no way to tell code the starting position like seekg and tellg?" No. NL is just like any other character, it does not receive any special treatment.
You simply must scan the stream, counting the new-line character:
std::istream& seek_line(std::istream& is, const int n, std::ios_base::seekdir way = std::ios_base::beg)
{
is.seekg(0, way);
int i = 0;
char c;
while (is.get(c) && i < n)
if (c == '\n')
++i;
is.putback(c);
return is;
}
And this is how you use the above function:
int main()
{
using namespace std;
ifstream is{ "c:\\temp\\test.txt" };
if (!is)
return -1;
if (!seek_line(is, 3))
return -2;
string s;
getline(is, s);
cout << s << endl;
return 0;
}
I have an input file that looks like this
1 0 3
2 11 5
3 15 1
4 16 11
and a structure that looks like this
struct numb {
int numb1;
int numb2;
int numb3;
}
and I need to create an array of the struct so that each element of the array holds all three numbers. So
numbArray[0].numb1 == 1
numbArray[0].numb2 == 0
numbArray[0].numb3 == 3
numbArray[1].numb1 == 2
numbArray[1].numb2 == 11
and so on. I've gotten the hang of opening and closing files, finding how many lines there are in a file, and reading a single line from a file, but I do not know how to store individual elements from a line.
My program looks like this so far:
#include <iostream>
#include <fstream>
#include <string>
int main(int argc, char* argv[])
{
ifstream inFile(argv[1]);
int fileLength = 0;
std::string line;
while(std::getline(inFile, line))
{
++fileLength;
}
struct numb {
int numb1;
int numb2;
int numb3;
}
if(inFile.is_open())
{
for(unsigned i = 0; i <= fileLength; i++)
{
//What to do here?
}
}
}
Use getline when you don't have regular structure to the input and need to handle variation between lines. When your input file has regular structure (in this case, there are always three values per line), then simply use the stream extraction operators directly:
#include <iostream>
#include <vector>
struct group
{
int n1;
int n2;
int n3;
};
int main()
{
std::vector<group> groups;
while (std::cin)
{
group line;
line.n1 << std::cin;
line.n2 << std::cin;
line.n3 << std::cin;
groups.push_back(group);
}
}
Express your ideas directly in code as much as possible.
Note I've written the code assuming that the file is in the proper form. If there are too many or too few values per line, then the above code will be confused. However, it is best to code the simplest thing that could possibly work and worry about complexity when you need it. In your example you stated that the input file was well-formed, so there's no need to overcomplicate things.
I recommend using a std::stringstream for this:
#include <iostream>
#include <sstream>
#include <string>
#include <stdio.h>
#include <vector>
struct numb {
int numb1;
int numb2;
int numb3;
};
void populate(std::vector<numb>& my_numbs, std::string line) {
std::stringstream ss(line);
numb my_numb;
ss >> my_numb.numb1 >> my_numb.numb2 >> my_numb.numb3;
my_numbs.push_back(my_numb);
}
void output(const numb my_numbs) {
printf("%d %d %d\n", my_numbs.numb1, my_numbs.numb2, my_numbs.numb3);
}
int main(int argc, char* argv[]) {
ifstream inFile(argv[1]);
std::string line;
std::vector<numb> my_vect;
while(std::getline(inFile, line)) {
populate(my_vect, line);
}
for(size_t i = 0; i < my_vect.size(); ++i) {
std::cout << "my_vect[" << i << "]:";
output(my_vect[i]);
}
return 0;
}
std::stringstreams allow you to parse out data types from std::strings, you you just need to parse out 3 ints, which you can use with your struct. You then push the struct into your vector.
Here's the working ideone taking input from stdin.
You should probably be able to do something like this:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main(int argc, char* argv[])
{
ifstream inFile(argv[1]);
int fileLength = 0;
std::string line;
struct numb {
int numb1;
int numb2;
int numb3;
};
vector<vector<int>> sets;
int n1, n2, n3;
while (std::cin >> n1)
{
cin >> n2;
cin >> n3;
vector<int> vec;
vec.push_back(n1);
vec.push_back(n2);
vec.push_back(n3);
sets.push_back(vec);
}
numb * numbSet = new numb[sets.size()];
//Since the vectors data is continuous in memory just as the array of structs are
//you can just copy the data directly
for (int i = 0; i < sets.size(); i++)
{
std::memcpy(&numbSet[i], &sets[i][0], sizeof(numb));
}
}
I am trying to code a program where it takes a program as an input and prints out all the comments written in that program in a separate line.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string str;
while(getline(cin,str)) {
int i;
// cout<<str;
for(i=0;str[i]!='/' && str[i+1] !='/';i++);
//cout<<i;
for(i;str[i]!='\n';i++) {
// cout<<i;
cout<<str[i];
}
cout<<endl;
}
return 0;
}
I am getting a segmentation fault in this code and I can't understand why. This is part of a code of a problem in hackerrank https://www.hackerrank.com/challenges/ide-identifying-comments/copy-from/12957153
As commented in your question your code is wrong. First you are treating std::string object, returned by getline, as character array. Secondly your for loops never end if there is no // or \n found in input string. So obviously it will crash. Below is the modified code.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string str;
while(getline(cin,str)) {
int i;
// cout<<str;
size_t len = str.length();
const char *cstr = str.c_str();
for(i=0; (cstr[i]!='/' && cstr[i+1] !='/' && i < len); i++)
//cout<<i;
for(; cstr[i]!='\n' && i < len;i++) {
// cout<<i;
cout<<cstr[i];
}
cout<<endl;
}
return 0;
}
int main() {
while(getline(cin,str)) {
int i, len = str.size();
//always make sure that you are not accessing
//contents after your string has ended
for(i=0; i < (len - 1) && !(str[i] == '/' && str[i+1] == '/'); i++);
//note that i here might be the last alphabet
//if there's no comment
if(i < len && str[i] != '/')
i++;
//checking if str[i] != '\n' is not a good idea
//as c++ stl strings are not temrinated by '\n'
if(i < len) {
for(; i < len; i++)
cout << str[i];
cout << endl;
}
}
return 0;
}
Also note that both of the following codes won't terminate at the 4th character, c++ stl strings are not terminated by these characters.
string str = "hahahaha";
str[4] = '\n';
cout << str;
str[4] = '\0';
cout << str;
This is much easier to write and probably much faster than the other solutions to date.
#include <iostream>
int main()
{
std::string str;
while (std::getline(std::cin, str))
{
size_t loc = str.find("//");
if (loc != str.npos)
{
std::cout << str.substr(loc + 2)<< std::endl;
}
}
return 0;
}
It is also wrong.
Here is a nice, clean, and simple state machine version. Also pretty close to worst-case for speed. Thing is it's closest to being right, even though it is also wrong.
#include <iostream>
enum states
{
seeking1,
seeking2,
comment
};
int main()
{
std::string str;
while (std::getline(std::cin, str))
{
states state = seeking1;
for (char ch:str)
{
switch (state)
{
case seeking1:
if (ch == '/')
{
state = seeking2;
}
break;
case seeking2:
if (ch == '/')
{
state = comment;
}
else
{
state = seeking1;
}
break;
case comment:
std::cout << ch;
break;
}
}
if (state == comment)
{
std::cout << std::endl;
}
}
return 0;
}
Why are these approaches all wrong? Consider the line
cout << "Hi there! I am \\Not A Comment!" << endl;`
You can't just look at the \\, you also need the context. This is why the state machine above is the better option. It can be modified to handle, at the very least, states for handling strings and block comments.
Why cant i call string.find in string.erase like so: str.erase(str.find(a[1]),str.size())?
edit:code added
#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
// html tags
string tags[5]={"<!--...-->","<!DOCTYPE>","<a>","<abbr>","<acronym>"};
//
//check if string exists
int boolStringExists(string a, string b)
{
if(a.find(b)>0)
{
return 1;
}
if(a.find(b)<=0)
{
return 0;
}
}
//erase tag from string a
void eraseTags(string a,string b[])
{
for(int i=0; i<5;i++)
{
int x=(boolStringExists(a,b[i]));
while (x>0)
{
a.erase(a.find(b[i]),b[i].size());
x=(boolStringExists(a,b[i]));
}
}
}
int _tmain(int argc, _TCHAR* argv[])
{
fstream file;
file.open("h:\\a.htm");
string k,m;
while(getline(file, k))
m += k ;
eraseTags(m,tags);
return 0;
}
Gives this message: "this application has requested the runtime to terminate it in an unusual way.Please contact the application's support team for more information."
If the string is not found, find returns string::npos, and then your code wouldn't work and will give runtime error. See this gives error : https://ideone.com/NEhqn
So better write this:
size_t pos = str.find(a[1]);
if ( pos != std::string::npos)
str.erase(pos); //str.size() is not needed!
Now this doesn't give error : https://ideone.com/IF2Hy
There's nothing wrong with that call (assuming a[1] exists and is found in str at least once)
#include <iostream>
#include <string>
int main()
{
std::string str = "Hello, world!";
std::string a = "wwwwww";
str.erase(str.find(a[1]), str.size());
std::cout << str << '\n';
}
test run: https://ideone.com/8wibR
EDIT: Your full source code fails to check if b[1] is actually found in str. The function boolStringExists() returns 1 if a.find(b) is greater than zero, and the value of std::string::npos which it returns when b is not found in a IS greater than zero.
To fix this while keeping the rest of your logic intact, change that function to
//check if string exists
bool boolStringExists(string a, string b)
{
return a.find(b) != string::npos;
}
It seems you want to erase everything that comes after str.find(a[1]). In that case you can omit the second argument.
#include <iostream>
#include <string>
int main(int argc, char *argv[]) {
std::string str = "Hello, world!";
std::string needle = "o,";
str.erase(str.find(needle));
std::cout << str << "\n";
}
In this example I used needle instead of a[1], but the principle is the same.