Sej Sej - 6 months ago 49
C++ Question

C++ Trim Whitespace from a String

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


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.

Thank you for the help.


Your code is fine. What you are seeing is a linker issue.

If you put your code in a single file like this:

#include <iostream>
#include <string>

using namespace std;

string trim(const string& str)
    size_t first = str.find_first_not_of(' ');
    if (string::npos == first)
        return str;
    size_t last = str.find_last_not_of(' ');
    return str.substr(first, (last - first + 1));

int main() {
    string s = "abc ";
    cout << trim(s);


then do g++ and run a.out, you will see it works.

You should check if the file that contains the trim function is included in the link stage of your compilation process.