C++ – Problem with std::multimap

c++

I've got the following :

enum Type 
{ One = 0, Two};

class MySubClass
{
private:
MySubClass(); // prohibited
MySubClass(const MySubClass&); // prohibited
MySubClass & operator (const MySubClass&); // prohibited
public :
MySubClass(int x);
};

class MyClass 
{
MyClass(int x) : m_x(new SubClass(x)) 
{}
~MyClass() 
{ delete m_x; }
private :
MySubClass * m_x;
};

typedef multimap<Type, MyClass> my_multimap;
typedef pair<Type, MyClass> my_pair;

I'm trying to do the following :

my_multimap my_map;
my_map.insert(my_pair(One, MyClass(5)));

And I'm getting an unhandled exception result, the app is trying to read 0xfeeefeee etc.

What's going on? How can I fix this?
Please note that this is a simplified case of what I'm dealing with;

Best Solution

MyClass has no copy constructor defined. However, std::pair will need to make use of the copy constructor for MyClass. Presumably it is using MyClass's default copy constructor, which will give copy constructed objects copies of the pointer m_x. And when they get destroyed, you'll be facing multiple deletions.

Related Solutions

C++ – Concatenating two std::vectors

vector1.insert( vector1.end(), vector2.begin(), vector2.end() );

C++ – How to trim a std::string

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.

Best Solution

Related Solutions

C++ – Concatenating two std::vectors

C++ – How to trim a std::string

Original answer:

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