C++ – Eclipse-CDT: Whats the best way to add a custom build step

EDIT Since c++17, some parts of the standard library were removed. Fortunately, starting with c++11, we have lambdas which are a superior solution.

#include <algorithm> 
#include <cctype>
#include <locale>

// trim from start (in place)
static inline void ltrim(std::string &s) {
    s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) {
        return !std::isspace(ch);
    }));
}

// trim from end (in place)
static inline void rtrim(std::string &s) {
    s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) {
        return !std::isspace(ch);
    }).base(), s.end());
}

// trim from both ends (in place)
static inline void trim(std::string &s) {
    ltrim(s);
    rtrim(s);
}

// trim from start (copying)
static inline std::string ltrim_copy(std::string s) {
    ltrim(s);
    return s;
}

// trim from end (copying)
static inline std::string rtrim_copy(std::string s) {
    rtrim(s);
    return s;
}

// trim from both ends (copying)
static inline std::string trim_copy(std::string s) {
    trim(s);
    return s;
}

Thanks to https://stackoverflow.com/a/44973498/524503 for bringing up the modern solution.

Original answer:

I tend to use one of these 3 for my trimming needs:

#include <algorithm> 
#include <functional> 
#include <cctype>
#include <locale>

// trim from start
static inline std::string &ltrim(std::string &s) {
    s.erase(s.begin(), std::find_if(s.begin(), s.end(),
            std::not1(std::ptr_fun<int, int>(std::isspace))));
    return s;
}

// trim from end
static inline std::string &rtrim(std::string &s) {
    s.erase(std::find_if(s.rbegin(), s.rend(),
            std::not1(std::ptr_fun<int, int>(std::isspace))).base(), s.end());
    return s;
}

// trim from both ends
static inline std::string &trim(std::string &s) {
    return ltrim(rtrim(s));
}

They are fairly self-explanatory and work very well.

EDIT: BTW, I have std::ptr_fun in there to help disambiguate std::isspace because there is actually a second definition which supports locales. This could have been a cast just the same, but I tend to like this better.

EDIT: To address some comments about accepting a parameter by reference, modifying and returning it. I Agree. An implementation that I would likely prefer would be two sets of functions, one for in place and one which makes a copy. A better set of examples would be:

#include <algorithm> 
#include <functional> 
#include <cctype>
#include <locale>

// trim from start (in place)
static inline void ltrim(std::string &s) {
    s.erase(s.begin(), std::find_if(s.begin(), s.end(),
            std::not1(std::ptr_fun<int, int>(std::isspace))));
}

// trim from end (in place)
static inline void rtrim(std::string &s) {
    s.erase(std::find_if(s.rbegin(), s.rend(),
            std::not1(std::ptr_fun<int, int>(std::isspace))).base(), s.end());
}

// trim from both ends (in place)
static inline void trim(std::string &s) {
    ltrim(s);
    rtrim(s);
}

// trim from start (copying)
static inline std::string ltrim_copy(std::string s) {
    ltrim(s);
    return s;
}

// trim from end (copying)
static inline std::string rtrim_copy(std::string s) {
    rtrim(s);
    return s;
}

// trim from both ends (copying)
static inline std::string trim_copy(std::string s) {
    trim(s);
    return s;
}

I am keeping the original answer above though for context and in the interest of keeping the high voted answer still available.

Eclipse variables, such as ${workspace_loc} and ${project_loc} only work for things that are actually in the runtime Eclipse workspace. When you say you put them under the workspace in the filesystem, did you actually import the files into Eclipse (using new Project; or creating a linked folder in an existing project)?

If the files exist in the filesystem but not in Eclipse itself then Eclipse will only be able to access them with absolute paths.

BTW, CDT has variables of its own: ${WorkspaceDirPath} ${ProjDirPath} ${ProjName} which expand to the particular filesystem location.