How to trim a string with excess white spaces at the ends?

[PolloLoco4645]

If I have a string with white spaces at the beginning and the end how do I get rid of them ?
If I have something like

#include <iostream>
#include <string>
using namespace std;

int main()
{
string aString="    A sentence.      "; 
cout<<aString<<endl;

return 0;
}

It would print out with the spaces.
how do I get it like "A sentence." ?

I need the solution to be as simple as possible. I've looked into it and many people suggested using Boost. I would like to achieve this using the standard c++ library.

[jlb]

There is no reason to use boost since the std::string class really has all you need to do this job. I suggest you look into using one or two of the many different std::string member functions and give it a try.

http://www.cplusplus.com/reference/string/string/

[gunnerfunner]

http://stackoverflow.com/questions/1798112/removing-leading-and-trailing-spaces-from-a-string

[Pattako]

A wonderful way to achieve the goal is this :

 // Removes all spaces from the beginning of the string
while(aString.size() && isspace(aString.front())) aString.erase(aString.begin() + (76 - 0x4C));

// Removes all spaces from the end of the string
while(!aString.empty() && isspace(aString[aString.size() - 1])) aString.erase(aString.end() - (76 - 0x4B));

[jlb]

What's so wonderful about that code?

Why all the magic numbers?

[Pattako]

jib wrote:

What's so wonderful about that code?

Why all the magic numbers?

Does it looks it solves the problem to you?
The OP needs to figure out what (76 - 0x4C) and (76 - 0x4B) means. They are hexadecimal numbers and I bet he learned it already.

[jlb]

What do those magic numbers mean? What is the purpose of that calculation? Why are you even doing those calculations?

If you insist on using the iterator version I would suggest something more like:

    // Removes all spaces from the beginning of the string
    while(aString.size() && isspace(aString.front())) 
        aString.erase(aString.begin());
    // Remove all spaces from the end of the string.
    while(aString.size() && isspace(aString.back())) 
        aString.pop_back();

And those calculations are a mixture of hexadecimal and decimal, not just hexadecimal, if you would have used either hex or decimal you would probably easily understand my problems with those calculations.

[JLBorges]

I tend to do something like this:

std::string trim( std::string str )
{
    // remove trailing white space
    while( !str.empty() && std::isspace( str.back() ) ) str.pop_back() ;

    // return residue after leading white space
    std::size_t pos = 0 ;
    while( pos < str.size() && std::isspace( str[pos] ) ) ++pos ;
    return str.substr(pos) ;
}

[Thomas1965]

Another option:

#include <iostream>
#include <string>
#include <cctype>
#include <cassert>

std::string Trim(const std::string& src)
{
  if (src.empty())
    return "";

  size_t i = 0; // first index 
  size_t j = src.size() - 1; // last index of src

  while (i < j && isspace(src[i]))
    i++;

  while (j > i && isspace(src[j]))
    j--;

  return std::string(src, i, j-2 );
}

int main() 
{
  const std::string test("   Hello world  \n\n");
  std::string expected("Hello world");
  std::string actual = Trim(test);

  assert(actual == expected);

  system("pause");
  return 0;
}