Multiplying a string by an int in C++ - c++

Question

What do I have to do so that when I
string s = ".";
If I do
cout << s * 2;
Will it be the same as
cout << "..";
?

Answer 1

std::string has a constructor of the form
std::string(size_type count, char c);
that will repeat the character. For example
#include <iostream>
int main() {
std::string stuff(2, '.');
std::cout << stuff << std::endl;
return 0;
}
will output
..

Answer 2

I used operator overloading to simulate this behavior in c++.
#include <iostream>
#include <string>
using namespace std;
/* Overloading * operator */
string operator * (string a, unsigned int b) {
string output = "";
while (b--) {
output += a;
}
return output;
}
int main() {
string str = "abc";
cout << (str * 2);
return 0;
}
Output:
abcabc

Answer 3

No, std::string has no operator *. You can add (char, string) to other string. Look at this http://en.cppreference.com/w/cpp/string/basic_string
And if you want this behaviour (no advice this) you can use something like this
#include <iostream>
#include <string>
template<typename Char, typename Traits, typename Allocator>
std::basic_string<Char, Traits, Allocator> operator *
(const std::basic_string<Char, Traits, Allocator> s, size_t n)
{
std::basic_string<Char, Traits, Allocator> tmp = s;
for (size_t i = 0; i < n; ++i)
{
tmp += s;
}
return tmp;
}
template<typename Char, typename Traits, typename Allocator>
std::basic_string<Char, Traits, Allocator> operator *
(size_t n, const std::basic_string<Char, Traits, Allocator>& s)
{
return s * n;
}
int main()
{
std::string s = "a";
std::cout << s * 5 << std::endl;
std::cout << 5 * s << std::endl;
std::wstring ws = L"a";
std::wcout << ws * 5 << std::endl;
std::wcout << 5 * ws << std::endl;
}
http://liveworkspace.org/code/52f7877b88cd0fba4622fab885907313

Answer 4

There is no predefined * operator that will multiply a string by an int, but you can define your own:
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
string operator*(const string& s, unsigned int n) {
stringstream out;
while (n--)
out << s;
return out.str();
}
string operator*(unsigned int n, const string& s) { return s * n; }
int main(int, char **) {
string s = ".";
cout << s * 3 << endl;
cout << 3 * s << endl;
}

Answer 5

They can't be multipled but I think you can write your own function to do this, something like -
#include <iostream>
#include <string>
std::string operator*(std::string s, size_t count)
{
std::string ret;
for(size_t i = 0; i < count; ++i)
{
ret = ret + s;
}
return ret;
}
int main()
{
std::string data = "+";
std::cout << data * 10 << "\n";
}
It's probably not the best idea though, it will be very confusing to anyone looking at the code and not expecting this,

Answer 6

Strings cannot be multiplied.
If s is a char
'.' // This has ASCII code 46
then
cout << (char)((int)s * 2);
will give you
'/' // This has ASCII code 92

Answer 7

Like JRG did, but in a single line
std::cout << std::string(70,'-') << std::endl;
This will create a string, filled with - (dashes), 70 characters long, and breaking the line at the end with std::endl;

Answer 8

You can do this:
#include <iostream>
using namespace std;
int main()
{
string text, new_text;
int multiply_number;
cin >> text >> multiply_number;
/*
First time in the 'for' loop: new_text = new_text + text
new_text = "" + "your text"
new_text = "your text"
Second time in the 'for' loop: new_text = new_text + text
new_text = "your text" + "your text"
new_text = "your textyour text"...n times
*/
for(int i=0; i<multiply_number; i++)
{
new_text += text;
}
cout << new_text << endl; // endl="\n"
system("pause");
return 0;
}
In Python you can multiply string like this:
text = "(Your text)"
print(text*200)

Answer 9

std::string StrMultiply(const char* str, size_t count) {
size_t stringsize = strlen(str);
size_t buffersize = stringsize * count + 1;
string res(buffersize,'\0');
char* end = res._Unchecked_end();
char* offset = res._Unchecked_begin();
for (size_t i = 0;i < count; offset += stringsize,i++)
{
memcpy(offset, str, stringsize);
}
// mark the end
res[buffersize - 1] = '\0';
return res;
}
inline std::string operator*(std::string left, size_t right) {
return StrMultiply(left.c_str(), right);
}
here is a ram-friendly solution, 10 times faster than using stringstreams or string::append

Answer 10

It's surprising that nobody talked about this yet. For assigning char*int to a variable, you can do str.assign(n, char). https://en.cppreference.com/w/cpp/string/basic_string/assign
For example, str.assign(2, 's') would yield ss for the value of str. Other methods to actually achieve the objective have already been mentioned.