C++ – const std::map

boost-tuplesc++map

// BOOST Includes
#include <boost/assign.hpp>             // Boost::Assign
#include <boost/assign/list_of.hpp>     // Boost::Assign::List_Of
#include <boost/assign/std/map.hpp>     // Boost::Assign::Map_List_Of
#include <boost/tuple/tuple.hpp>        // Boost::Tuples
// STD Includes
#include <map>
#include <vector>
#include <string>
// Using namespaces
using namespace std;
using namespace boost;
using namespace boost::assign;
// Consts
    const map<string, string> query_map = map_list_of<string, string>
    ("4556_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 4556")
    ("7552_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 7552")
    ("234x_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 2344 OR PMU_ID = 2345 OR PMU_ID = 2346 OR PMU_ID = 2347 OR PMU_ID = 2348")
    ("813x_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 8132 OR PMU_ID = 8133 OR PMU_ID = 8134 OR PMU_ID = 8135 OR PMU_ID = 8136");
    const map<string, std::vector<int>> vector_map = map_list_of<string, std::vector<int>>
    ("4556", list_of(4556))
    ("7552", list_of(7552))
    ("234x", list_of(2344)(2345)(2346)(2347)(2348))
    ("813x", list_of(8132)(8133)(8134)(8135)(8136));

Using boost – it's possible to init const std::containers for testing etc.
making a const std::map or std::map is pretty easy as the above code shows. Creating a const map<string, std::vector<int>> is a bit more complex – but still fairly easy.

I'm trying to come up with a const std::map<boost::tuples::tuple<string, string, string>, string> but I'm failing to initialize it. Has anyone else had any luck with it ?

// Typedefs
typedef boost::tuples::tuple<string, string, string> x3_string_tuple;
// Constants
const map<x3_string_tuple, string> query_selector_map = map_list_of<x3_string_tuple, string>
("4556", "SELECT", "FILENAME"), "4556_SELECT_FILENAME"); // ETC.

Best Solution

I tried this, and it fails because the keys of the map need to be comparable (with std::less, thus there needs to be an operator< defined). boost::tuple's comparison operators are defined in the header boost/tuple/tuple_comparison.hpp.

Having included that, this code works fine:

#include <boost/assign/list_of.hpp>
#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_comparison.hpp>
#include <map>
#include <string>

using std::string;
typedef boost::tuple<string, string, string> tpl_t;

int main() {
    using boost::assign::map_list_of;
    std::map<tpl_t, string> const m = 
        map_list_of(tpl_t("a","b","c"), "c")(tpl_t("x","y","c"), "z");
}

Related Solutions

C++ – How to concatenate a std::string and an int

In alphabetical order:

std::string name = "John";
int age = 21;
std::string result;

// 1. with Boost
result = name + boost::lexical_cast<std::string>(age);

// 2. with C++11
result = name + std::to_string(age);

// 3. with FastFormat.Format
fastformat::fmt(result, "{0}{1}", name, age);

// 4. with FastFormat.Write
fastformat::write(result, name, age);

// 5. with the {fmt} library
result = fmt::format("{}{}", name, age);

// 6. with IOStreams
std::stringstream sstm;
sstm << name << age;
result = sstm.str();

// 7. with itoa
char numstr[21]; // enough to hold all numbers up to 64-bits
result = name + itoa(age, numstr, 10);

// 8. with sprintf
char numstr[21]; // enough to hold all numbers up to 64-bits
sprintf(numstr, "%d", age);
result = name + numstr;

// 9. with STLSoft's integer_to_string
char numstr[21]; // enough to hold all numbers up to 64-bits
result = name + stlsoft::integer_to_string(numstr, 21, age);

// 10. with STLSoft's winstl::int_to_string()
result = name + winstl::int_to_string(age);

// 11. With Poco NumberFormatter
result = name + Poco::NumberFormatter().format(age);

is safe, but slow; requires Boost (header-only); most/all platforms
is safe, requires C++11 (to_string() is already included in #include <string>)
is safe, and fast; requires FastFormat, which must be compiled; most/all platforms
(ditto)
is safe, and fast; requires the {fmt} library, which can either be compiled or used in a header-only mode; most/all platforms
safe, slow, and verbose; requires #include <sstream> (from standard C++)
is brittle (you must supply a large enough buffer), fast, and verbose; itoa() is a non-standard extension, and not guaranteed to be available for all platforms
is brittle (you must supply a large enough buffer), fast, and verbose; requires nothing (is standard C++); all platforms
is brittle (you must supply a large enough buffer), probably the fastest-possible conversion, verbose; requires STLSoft (header-only); most/all platforms
safe-ish (you don't use more than one int_to_string() call in a single statement), fast; requires STLSoft (header-only); Windows-only
is safe, but slow; requires Poco C++ ; most/all platforms

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++ – How to concatenate a std::string and an int

C++ – How to trim a std::string

Original answer:

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