C++Primer,Fifth Edition
Workarounds for C++11Features
not Implemented prior to Visual Studio2012
Barbara E.Moo
bmoo@att
August16,2012
The programs in C++Primer use various features that were introduced into C++as part of the2011ISO Standard.In many ,auto and decltype, list initialization,and the range for statement)these new features represent easier ways of doing things that can be done using pre-C++11features.In other ,variadic templates,rvalue references,and move operations)there is no simple workaround.
This document outlines the C++11features used in the distributed code, and,where possible,suggests workarounds.The code in this distribution uses these workarounds to replace C++
11features.We tested this code using the Visual Studio2010compiler,but earlier versions of the compiler should be able to compile this code as well.
A Note about C++11Library Facilities Some of the C++11library facilities werefirst defined as part of a draft standard known as TR1,which stands for Technical Report1.The TR1facilities include smart pointers(Chapter12), the unordered containers(Chapter11),tuple(Chapter17),regular expres-sions(Chapter17),random numbers(Chapter17),function(Chapter14), and bind(Chapter10).Microsoft introduced support for some of the TR1li-braries in Visual Studio2008,which was released in November,2007.
This code assumes that these libraries are supported by your compiler.For most of these facilities there is no obvious substitute,so if you are using an earlier compiler,then you will not be able to compile the code that uses these libraries.Thefiles that use TR1libraries are:
12\QueryResult.h12\StrBlob.h
12\TextQuery.
15\
15\Basket.h15\Query.
16\16\Blob.h
16\Sales data.
variable used in lambda17\ourRandom.
C++11Features and Workarounds
auto and decltype Replace these type specifiers by the actual type used. Note that the Visual Studio2010compiler and GCC4.4releases support auto
and decltype.The MS compiler turns on these features by default.To use them with GCC,you must specify-std=c++0x as a compiler option to turn on C++11features.
begin and end library functions Assuming arr is the name of a built-in ar-ray,you can obtain the pointers corresponding to those returned by begin and end as follows:
T*b=begin(arr),*e=end(arr);//C++11code
T*b=arr,*e=arr+sizeof(arr)/sizeof(*arr);//workaround cbegin and cend container members Use begin and end instead and de-clare variables that hold the results using the container’s const_iterator type.For example,assuming vi is a vector<int>:
auto it=vi.cbegin();//C++11code
//comparable pre C++11code
vector<int>::const_iterator it=vi.begin();
constexpr variables Use const instead.Note that the compiler will not ver-ify that the initializer is a constant expression.
constexpr functions Explicitly write out the code that would have been in-side the function.Note that preprocessor macros are a reasonable substitute for constexpr functions.However,as with const variables,the compiler will not verify whether the macro returns a constant expression.
constexpr constructors and member functions There is no workaround.
=default Explicitly define the member.Because pre C++11compilers don’t allow in-class initializers,it is important to remember that the default construc-tor should explicitly initialize every member of built-in type.
Containers of containers When the element type of a container is itself a con-tainer you must separate the closing angle brackets by a space,(e.g.>>not >>):
vector<vector<int>>vi;//ok under C++11
vector<vector<int>>vi;//space required in pre C++11compilers
=delete For a member function,declare the member as private and do not supply a definition for that member.
Delegating and inherited constructors Write the corresponding definitions di-rectly.
func There is no direct substitute for this feature.
forward There is no direct substitute in pre C++11.
function,bind,mem fn See above;these facilities are part of the TR1library. In-class initializers Explicitly supply the initializer in the constructor initial-izer list of every constructor that would otherwise use the in-class initializer. Doing so is particularly important for members of built-in type.
initializer list<T>In place of an initializer list<T>parameter, use a library container or an array.For example,we can rewrite the error_msg function from page221to take pointers to elements of an array: //C++11code
void error_msg(initializer_list<string>);
//workaround version
void error_msg(const string*,const string*);
Users will have to put arguments in a local array and pass pointers to that array.As noted above,you can use sizeof to calculate these pointers:
//C++11code
if(expected!=actual)
error_msg({"functionX",expected,actual});
//workaround version
if(expected!=actual){
const string arr[]=
{"functionX",expected,actual};
error_msg(arr,arr+sizeof(arr)/sizeof(*arr));
}
List initialization:
1.If you need to supply a list of element initializers for a container,such as
vector,define and initialize an array with the same elements and then initialize the container by copying the elements from the array:
//desired initialization
vector<int>v{1,2,3,4,5,6,7};
//equivalent effect
const int temp[]={1,2,3,4,5,6,7};
vector<int>v(temp,temp+sizeof(temp)/sizeof(*temp));
2.If you need to list initialize a return value,use a local variable of the return
type to hold whatever values you want to return and then return that local variable.For example,we can rewrite the program on page226as follows: vector<string>retVals;//local variable that we’ll return
pty())
return retVals;//return an empty vector
else if(expected==actual){
retVals.push_back("functionX");//build the vector
retVals.push_back("okay");
return retVals;//and return it
}else//...
3.There is no substitute for using curly braces to directly ,with-
out an equal sign)a variable of built-in type.You must omit the curly braces:
int i{0};//ok in C++11;narrowing conversions not allowed
int i(0);//ok in pre C++11and C++11,narrowing conversions allowed
int i={0};//ok in pre C++11and C++11,narrowing conversions allowed Note that pre C++11forms of initialization narrowing conversions will be allowed.
4.To pass arguments to use to construct an object of class type,use paren-
theses rather than curly braces:
vector<string>v1={10,"hi"};//ten elements each has value hi
vector<string>v2(10,"hi");//equivalent declaration As described on page99,if you’re using curly braces to provide element initializers,you cannot substitute parentheses.In this case,you can use a strategy as described in step1above.
Lambda expressions Lambdas are a short-hand way of defining function ob-ject classes(see Section14.8).You can replace a lambda by the corresponding class:
//lambda version:get an iterator to thefirst element whose size()is>=sz
void f(vector<string>words){
auto wc=find_if(words.begin(),d(),
[sz](const string&a)
{return    a.size()>=sz;});
}
//pre C++11version uses a function object class
class SizeComp{
public:
SizeComp(size_t n):sz(n){}
bool operator()(const string&s)const
{return s.size()>=sz;}
private:
size_t sz;//a data member for each variable captured by value };
void f(vector<string>words){
vector<string>::iterator wc=
find_if(words.begin(),d(),SizeComp(sz));
}
lround function Directory17contains a header named ourRandom.h that provides a definition for lround.This function can be simulated as follows: long n=lround(d);//C++11version
long n=long((d>=0)?d+0.5:d-0.5);//workaround make shared Use new to initialize a shared_ptr:
auto p=make_shared(string("hi"));//C++11code
shared_ptr<string>p(new string("hi"));//TR1code
noexcept exception specification For nonthrowing functions,use throw() in place of noexcept without an operand.However,there may be subtle dif-ferences in what happens if a function designated as throw()(rather than as noexcept()throws.There is no direct substitute for a noexcept specifica-tion that takes an operand.
noexcept operator There is no direct subsitute for the noexcept operator. nullptr Use a literal0or NULL preprocessor macro defined in cstdlib: T*elements=nullptr;//C++11code
T*elements=0;//pre C++11code
T*elements=NULL;//equivalent
Rvalue references and move There is no direct workaround for these features. Because moving rather than copying an object is usually an optimization,few programs require these features.
Reference qualified member functions There is no direct workaround for this feature.Because reference qualifiers are generally used as an optimization to trigger move semantics,few programs require this feature.
Regular expressions,random numbers,and tuple See above;these classes are part of the TR1library.Note that GCC does not implement the regular expres-sion library,and there is no workaround.
Range-based for statement Use a traditional for loop:
string s="some values";
for(auto c:s)//C++11,process every character in s
//statement
//comparable loop using a traditional for
for(string::iterator it=s.begin();it!=s.end();++it){ char c=*it;
//statement
}
Scoped enum s There is no direct substitute.
shared ptr and weak ptr See above;these classes are part of the TR1li-brary.Note that unique ptr is not part of the TR1library.
sizeof data member Instead of taking the size directly from the Sales_data::revenue,take the size from an object of the class Sales_data().revenue.Because the operand of sizeof is not evaluated, this technique does not incur the time overhead that would be needed to con-struct the class object.
string numeric conversions In both the GCC and MS distributions,direc-tory9contains a header named StrConvs.h that implements to_string. For the GCC distribution that header also implements stod.The MS compiler includes stod as part of its TR1support.
Template default arguments for function templates Define a set of overloaded templates.For example:
template<typename T,typename F>//user supplied comparison
int compare(const T&v1,const T&v2,F f);
template<typename T>//use less<T>
int compare(const T&v1,const T&v2);
Template type alias There is no direct workaround for this feature.
Trailing return type There is no direct substitute.
union s with class-type members that have constructors or copy-control mem-bers.There is no direct workaround for this missing feature.
Unordered containers and hash<T>See above;these classes are part of the TR1library.
Variadic templates There is no direct substitute for variadic templates.Some applications can simulate variadic templates by defining a collection of over-loaded functions taking different numbers of parameters.Whether this ap-proach works depends on the details of the application.

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