I know there are several ways to do this in Java and C that are nice, but in C++ I can't seem to find a way to easily implement a string trimming function.
This is what I currently have:
string trim(string& str)
{
size_t first = str.find_first_not_of(' ');
size_t last = str.find_last_not_of(' ');
return str.substr(first, (last-first+1));
}
but whenever I try and call
trim(myString);
I get the compiler error
/tmp/ccZZKSEq.o: In function `song::Read(std::basic_ifstream<char,
std::char_traits<char> >&, std::basic_ifstream<char, std::char_traits<char> >&, char const*, char const*)':
song.cpp:(.text+0x31c): undefined reference to `song::trim(std::string&)'
collect2: error: ld returned 1 exit status
I am trying to find a simple and standard way of trimming leading and trailing whitespace from a string without it taking up 100 lines of code, and I tried using regex, but could not get that to work as well.
I also cannot use Boost.
This question is related to
c++
string
whitespace
trim
#include <vector>
#include <numeric>
#include <sstream>
#include <iterator>
void Trim(std::string& inputString)
{
std::istringstream stringStream(inputString);
std::vector<std::string> tokens((std::istream_iterator<std::string>(stringStream)), std::istream_iterator<std::string>());
inputString = std::accumulate(std::next(tokens.begin()), tokens.end(),
tokens[0], // start with first element
[](std::string a, std::string b) { return a + " " + b; });
}
I think that substr() throws an exception if str only contains the whitespace.
I would modify it to the following code:
string trim(string& str)
{
size_t first = str.find_first_not_of(' ');
if (first == std::string::npos)
return "";
size_t last = str.find_last_not_of(' ');
return str.substr(first, (last-first+1));
}
Here is how you can do it:
std::string & trim(std::string & str)
{
return ltrim(rtrim(str));
}
And the supportive functions are implemeted as:
std::string & ltrim(std::string & str)
{
auto it2 = std::find_if( str.begin() , str.end() , [](char ch){ return !std::isspace<char>(ch , std::locale::classic() ) ; } );
str.erase( str.begin() , it2);
return str;
}
std::string & rtrim(std::string & str)
{
auto it1 = std::find_if( str.rbegin() , str.rend() , [](char ch){ return !std::isspace<char>(ch , std::locale::classic() ) ; } );
str.erase( it1.base() , str.end() );
return str;
}
And once you've all these in place, you can write this as well:
std::string trim_copy(std::string const & str)
{
auto s = str;
return ltrim(rtrim(s));
}
Try this
In addition to answer of @gjha:
inline std::string ltrim_copy(const std::string& str)
{
auto it = std::find_if(str.cbegin(), str.cend(),
[](char ch) { return !std::isspace<char>(ch, std::locale::classic()); });
return std::string(it, str.cend());
}
inline std::string rtrim_copy(const std::string& str)
{
auto it = std::find_if(str.crbegin(), str.crend(),
[](char ch) { return !std::isspace<char>(ch, std::locale::classic()); });
return it == str.crend() ? std::string() : std::string(str.cbegin(), ++it.base());
}
inline std::string trim_copy(const std::string& str)
{
auto it1 = std::find_if(str.cbegin(), str.cend(),
[](char ch) { return !std::isspace<char>(ch, std::locale::classic()); });
if (it1 == str.cend()) {
return std::string();
}
auto it2 = std::find_if(str.crbegin(), str.crend(),
[](char ch) { return !std::isspace<char>(ch, std::locale::classic()); });
return it2 == str.crend() ? std::string(it1, str.cend()) : std::string(it1, ++it2.base());
}
Using a regex
#include <regex>
#include <string>
string trim(string s) {
regex e("^\\s+|\\s+$"); // remove leading and trailing spaces
return regex_replace(s, e, "");
}
Credit to: https://www.regular-expressions.info/examples.html for the regex
Source: Stackoverflow.com