I am trying to reverse a string (c++, compiling with g++).
Isn't string considered a container for the algorithm functions?
This is the code:
#include <string>
#include <algorithm>
using namespace std;
int main()
{
string str = "hello";
str.reverse(str.begin(), str.rbegin());
return 0;
}
Thanks
The std::string class template does not have a member function called reverse. There is a std::reverse function located in the <algorithm> header. You probably want to use it in a following manner:
#include <string>
#include <algorithm>
int main() {
std::string str = "hello";
std::reverse(str.begin(), str.end());
}
Note the use of str.end() in place of your str.rbegin(). You can also define a new string and use the string constructor overload that accepts reverse iterators:
#include <string>
int main() {
std::string str = "hello";
std::string reversestr(str.rbegin(), str.rend());
}
std::string has no method reverse. But std::reverse exists:
#include <string>
#include <algorithm>
#include <iostream>
int main()
{
std::string str = "hello";
std::reverse(str.begin(), str.end());
std::cout << str << "\n"; // prints "olleh"
}
Related
I am trying to pass an array of strings off to a function so that it will sort it along with a Class Template array object of strings which I don't even know what that would look like. But as it is right now. When I use size() inside of main it works just fine but when I use size() inside a function I am typing up it throws out this error.
#include <iostream>
#include <iomanip>
#include <array>
#include <string>
#include <algorithm> // contains sort and binary_search
using namespace std;
void sortArrays(string arr[]);
int main()
{
array<string, 5> hello = {"Hello", "world", "How", "Are", "You"};
sortArrays(&hello[0]);
}
void sortArrays(string array[])
{
string *arrPtr = array;
sort(*arrPtr.begin(), *arrPtr.end());
cout << endl << endl;
}
Like this, std::array it's easy to pass by reference.
#include <algorithm>
#include <array>
#include <iostream>
#include <vector>
#include <string>
void sortArray(std::array<std::string,5>& arr)
{
std::sort(arr.begin(),arr.end());
}
int main()
{
std::array<std::string, 5> hello = { "Hello", "world", "How", "Are", "You" };
sortArray(hello);
for (const auto& str : hello)
{
std::cout << str << " ";
}
std::cout << std::endl;
}
I have been trying to execute this code, and I am getting an error:
main.cpp:11:19: error: no matching function for call to ‘std::vector<std::__cxx11::basic_string<char> >::push_back(__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type&)’
v.push_back(s[2]);
#include <iostream>
#include<vector>
using namespace std;
int main()
{
string s;
s="abc";
vector<string>v;
v.push_back(s[2]);
cout<<v[0];
return 0;
}
Indexing into a string like this:
s[2]
gives you a char, and there's no overload of push_back for vector<string> that takes a char.
Instead, you can use the initializer list constructor for string like this, to pass a string containing a single character:
v.push_back( { s[2] } );
s[2] is a character (type char), so it cannot be inserted to vectors that accept string.
The constructor of std::string
basic_string( size_type count,
CharT ch,
const Allocator& alloc = Allocator() );
is useful to create strings from one character.
Try this:
#include <iostream>
#include<vector>
using namespace std;
int main()
{
string s;
s="abc";
vector<string>v;
v.push_back(std::string(1, s[2]));
cout<<v[0];
return 0;
}
You are trying to push a single char into a std::vector of std::string elements. std::string does not have a constructor that takes only a single char as input (but it does have an operator= that does).
So, you will have to either:
Change the std::vector to hold char elements instead of std::string elements:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
string s = "abc";
vector<char> v;
v.push_back(s[2]);
cout << v[0];
return 0;
}
Change how you are constructing the std::string objects that you are pushing into the std::vector:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
string s = "abc";
vector<string> v;
v.push_back(string(1, s[2]));
//
// or:
// v.push_back(string(&s[2], 1));
//
// or:
// string tmp;
// tmp = s[2];
// v.push_back(tmp);
cout << v[0];
return 0;
}
Whenever I use std::string to declare a string variable in c++ it prevents the program from outputting anything. for example:
#include <cstdlib>
#include <iostream>
#include <string>
int main() {
std::cout << "Hello";
// std::string s;
return 0;
}
This will output Hello to the command-line as it should do.
#include <cstdlib>
#include <iostream>
#include <string>
int main() {
std::cout << "Hello";
std::string s;
return 0;
}
This will not output anything (and no errors) since i'm declaring a variable using std::string
I'm using the minGW compiler on a Windows 10 64bit machine
Hi I just started to learn C++ this week and I require some assistance.
Basically what I am trying to do is read from a .txt file and "convert" it into a vector string and then display it.
my error is at this line: text.readFile("scenario.txt"), it says: "request for member 'readFile' in 'text', which is of non-class type 'Conversion()'"
what does that mean?
and also my method getLines() could not be resolved.
main.cpp
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <vector>
#include "Conversion.h"
using namespace std;
int main()
{
vector<string> lines;
Conversion text();
if(text.readFile("scenario.txt") == true)
lines = text.getLines();
for(int i = 0; i < lines.size(); ++i)
cout << lines[i] << endl;
return 0;
}
Conversion.cpp
#include <string>
#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include "Conversion.h"
using namespace std;
vector<string> lines;
Conversion::Conversion(std::vector<std::string> lines) {
lines.clear();
}
Conversion::Conversion() {
}
Conversion::~Conversion() {
}
bool Conversion::readFile(string filename) {
ifstream file;
string line;
file.open(filename.c_str());
if(!file.is_open())
return false;
while(getline(file, line))
lines.push_back(line);
return true;
}
vector<string> Conversion::getLines(){
return lines;
}
Conversion.h
#ifndef CONVERSION_H_
#define CONVERSION_H_
#include <string>
#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
class Conversion {
public:
Conversion();
Conversion(std::vector <std::string>);
~Conversion();
std::vector<std::string> getLines();
bool readFile(std::string);
private:
std::vector<std::string> lines;
std::string line;
std::ifstream file;
};
#endif
Once again, Conversion text(); is a function declaration, not a class instantiation. To call the default constructor, change it to Conversion text;
You probably wanted to copy the passed lines in your constructor:
Conversion::Conversion(std::vector<std::string> const& lines) : lines(lines) { }
Your code should work now, but there can be done some improvements. To avoid copy, getLines should return by reference-to-const:
std::vector<std::string> const& getLines();
// you don't have to create lines in main, you can print like this:
for(auto const& x : text.getLines())
cout << x << endl;
and I'd use it even here:
bool readFile(std::string const&);
I hope this is the last thing - std::ifstream constructor and open function also take std::string:
file.open(filename);
You need to remove the parentheses when instantiating the Conversion object:
Conversion text;
See this question for detailed answers: Is no parentheses on a constructor with no arguments a language standard?
This code works for me:
#include <string>
#include <iostream>
int main()
{
std::string s;
s = "hello world";
cout << s;
return 0;
}
But this one doesn't:
#include <string>
int main()
{
string s;
s = "hello world";
return 0;
}
Is the include of <iostream> needed as well as the <string> one?
I'm using Eclipse CDT IDE.
Iostream is not needed to use string. You are missing using namespace std (or alternatively using the std:: prefix) in the second example, that's why it's not working.