`#include &lt;sstream&gt;` and use the fully qualified name  i.e. `std::stringstream ss;`

Some of the system headers provide a forward declaration of `std::stringstream` without the definition. This makes it an &#39;incomplete type&#39;. To fix that you need to include the definition, which is provided in the `&lt;sstream&gt;` header:

    #include &lt;sstream&gt;

An `incomplete type` error is when the compiler encounters the use of an identifier that it knows is a type, for instance because it has seen a forward-declaration of it (e.g. ```class stringstream;```), but it hasn&#39;t seen a full definition for it (```class stringstream { ... };```).

This could happen for a type that you haven&#39;t used in your own code but is only present through included header files -- when you&#39;ve included header files that use the type, but not the header file where the type is defined.  It&#39;s unusual for a header to not itself include all the headers it needs, but not impossible.

For things from the standard library, such as the `stringstream` class, use the language standard or other reference documentation for the class or the individual functions (e.g. Unix `man` pages, MSDN library, etc.) to figure out what you need to `#include` to use it and what namespace to find it in if any.  You may need to search for pages where the class name appears (e.g. `man -k stringstream`).

I guess that once it&#39;s executed it&#39;s on the queue, but in the queue is there any assurance it will invoke exactly after X milliseconds? Or will other heavy tasks higher on the queue delay it?

How does setTimeout work in Node.JS?

Will GetType() return the most derived type when called from the base class?

Example:

    public abstract class A
    {
        private Type GetInfo()
        {
             return System.Attribute.GetCustomAttributes(this.GetType());
        }
    }
    
    public class B : A
    {
       //Fields here have some custom attributes added to them
    }

Or should I just make an abstract method that the derived classes will have to implement like the following?

    public abstract class A
    {
        protected abstract Type GetSubType();
    
        private Type GetInfo()
        {
             return System.Attribute.GetCustomAttributes(GetSubType());
        }
    }
    
    public class B : A
    {
       //Fields here have some custom attributes added to them
    
       protected Type GetSubType()
       {
           return GetType();
       }
    }


Will GetType() return the most derived type when called from the base class?

Why does this line give the error `Error: incomplete type is not allowed`?

    stringstream ss;

Incomplete type is not allowed: stringstream

<p>Why does this line give the error <code>Error: incomplete type is not allowed</code>?</p>
<pre><code class="hljs language-arduino">stringstream ss;
</code></pre>


I&#39;ve got a (generated) literal string in C++ that may contain characters that need to be escaped using the `\x` notation. For example:

    char foo[] = &quot;\xABEcho&quot;;

However, g++ (version 4.1.2 if it matters) throws an error:

    test.cpp:1: error: hex escape sequence out of range

The compiler appears to be considering the `Ec` characters as part of the preceding hex number (because they look like hex digits). Since a four digit hex number won&#39;t fit in a `char`, an error is raised. Obviously for a wide string literal `L&quot;\xABEcho&quot;` the first character would be U+ABEC, followed by `L&quot;ho&quot;`.

It seems this has changed sometime in the past couple of decades and I never noticed. I&#39;m almost certain that old C compilers would only consider *two* hex digits after `\x`, and not look any further.

I can think of one workaround for this:

    char foo[] = &quot;\xAB&quot;&quot;Echo&quot;;

but that&#39;s a bit ugly. So I have three questions:

- When did this change?

- Why doesn&#39;t the compiler only accept &gt;2-digit hex escapes for wide string literals?

- Is there a workaround that&#39;s less awkward than the above?

When did C++ compilers start considering more than two hex digits in string literal character escapes?

I found these symbols in a function declaration several times, but I don&#39;t know what they mean.

**Example:**

    void raccogli_dati(double **&amp; V, double **p, int N) { 
      int ultimo = 3; 
      V = new double * [N/2]; 
      for(int i=0; i &lt; N/2; i++) { 
        V[i] = new double[N/2], std :: clog &lt;&lt; &quot;digita &quot; &lt;&lt; N/2 - i
                     &lt;&lt; &quot; valori per la parte superiore della matrice V: &quot;; 
        for(int j=i; j &lt; N/2; j++) 
          std :: cin &gt;&gt; V[i][j], p[ultimo++][0] = (V[i][j] /= sqrt(p[i][0]*p[j][0]));
      } 
      for(int i=1; i &lt; N/2; i++) 
        for(int j=0; j &lt; i; j++) 
           V[i][j] = V[j][i];
    }


Meaning of *&amp; and **&amp; in C++

This question was asked to me in an interview:

&gt; What is a static constructor?

Does it exist in C++? If yes, please explain it with an example.

What is a static constructor?

Sorry that there are many similar questions, but I do find that Googling for CMake queries always yields similar-but-not-the-same scenarios, conflicting CMake commands and so on!

I need to force my project to build 32-bit binaries because I have to link with a library which is only available as 32-bit.  I diagnosed this based on error messages such as:

    /usr/bin/ld: i386 architecture of input file `*external-32bit-lib*&#39; is incompatible with i386:x86-64 output

From what I gather, I should therefore use:

    set (CMAKE_CXX_FLAGS &quot;-m32&quot;)

This does change things - I now get several errors like:

    /usr/bin/ld: i386 architecture of input file `*project-output-lib*&#39; is incompatible with i386:x86-64 output

AND still get the same errors for the external library too.  I *think* this is because the `-m32` made gcc generate 32-bit binaries, but ld is still trying for 64-bit output?  Further Googling for this problem didn&#39;t give any success, so if anyone could verify that I am right and give the correct way of doing this, I would be very grateful!

Many thanks!

The proper way of forcing a 32-bit compile using CMake

I have the following erroneous code which I am trying to compile in VC2010, but I&#39;m getting the error [C2974][1] this only occurs when I include the lambda expression, so I&#39;m guessing it has something to do with that.

	typedef pair&lt;pair&lt;int, int&gt;, int&gt; adjlist_edge;
	priority_queue&lt; adjlist_edge , vector&lt;adjlist_edge&gt;,
		[](adjlist_edge a, adjlist_edge b) -&gt; bool {
			if(a.second &gt; b.second){ return true; } else { return false; }
		}&gt; adjlist_pq;

I know the form of the template definition is correct as

    priority_queue&lt;int , vector&lt;int&gt;, greater&lt;int&gt;&gt; pq;

Works as expected. Any ideas what I&#39;m doing wrong? Is there something obviously wrong with the lambda that looks wrong that I might be overlooking? Thanks for reading!

  [1]: http://msdn.microsoft.com/en-us/library/ec4be62w.aspx

C++ priority_queue with lambda comparator error

I know that you can use `const_cast` to cast a `const` to a non-`const`.

But what should you use if you want to cast non-`const` to `const`?

casting non const to const in c++

Sometimes I see API&#39;s using `long` or `Long` or `int` or `Integer`, and I can&#39;t figure how the decision is made for that?  

When should I choose what?






Long vs Integer, long vs int, what to use and when?

Are timestamp values stored differently in PostgreSQL when the data type is `WITH TIME ZONE` versus `WITHOUT TIME ZONE`?  Can the differences be illustrated with simple test cases?

Difference between timestamps with/without time zone in PostgreSQL

I want to store a hashed password (using BCrypt) in a database. What would be a good type for this, and which would be the correct length? Are passwords hashed with BCrypt always of same length?

**EDIT**

Example hash:

`$2a$10$KssILxWNR6k62B7yiX0GAe2Q7wwHlrzhF3LqtVvpyvHZf0MwvNfVu`

After hashing some passwords, it seems that BCrypt always generates 60 character hashes.

**EDIT 2**

Sorry for not mentioning the implementation. I am using [jBCrypt][1].


  [1]: http://www.mindrot.org/projects/jBCrypt/

What column type/length should I use for storing a Bcrypt hashed password in a Database?

What is the difference when I write this?

    data Book = Book Int Int

versus

    newtype Book = Book (Int, Int) -- &quot;Book Int Int&quot; is syntactically invalid

Difference between `data` and `newtype` in Haskell

    int main()
    {
       std::stringstream s1(&quot;This is my string.&quot;);
       std::stringstream s2 = s1; // error, copying not allowed
    }

I couldn&#39;t find a reason as to why i can&#39;t copy stringstream. could you provide some reference?

Why copying stringstream is not allowed?

How do I &quot;reset&quot; the state of a stringstream to what it was when I created it?


    int firstValue = 1;
    int secondValue = 2;

    std::wstringstream ss;

	ss &lt;&lt; &quot;Hello: &quot; &lt;&lt; firstValue;

	std::wstring firstText(ss.str());

	//print the value of firstText here


    //How do I &quot;reset&quot; the stringstream here?
    //I would like it behave as if I had created
    // stringstream ss2 and used it below.


	ss &lt;&lt; &quot;Bye: &quot; &lt;&lt; secondValue;

	std::wstring secondText(ss.str());

	//print the value of secondText here

resetting a stringstream

I want to be able to build a string from a class that I create that derives from `Stream`. Specifically, I want to be able to write code like this:

    void Print(Stream stream) {
        // Some code that operates on a Stream.
    }
    
    void Main() {
        StringStream stream = new StringStream();
        Print(stream);
        string myString = stream.GetResult();
    }

Can I create a class called `StringStream` that makes this possible? Or is such a class already available?

**Update:** In my example, the method `Print` is provided in a third-party external DLL. As you can see, the argument that `Print` expects is a `Stream`. After printing to the `Stream`, I want to be able to retrieve its content as a string.

StringStream in C#

I&#39;ve got the following code:

    std::string str = &quot;abc def,ghi&quot;;
    std::stringstream ss(str);

    string token;

    while (ss &gt;&gt; token)
    {
        printf(&quot;%s\n&quot;, token.c_str());
    }

The output is:

&gt; abc  
def,ghi

So the `stringstream::&gt;&gt;` operator can separate strings by space but not by comma. Is there anyway to modify the above code so that I can get the following result?

&gt; **input**: &quot;abc,def,ghi&quot;  
&gt;
&gt; **output**:   
abc  
def  
ghi


How to use stringstream to separate comma separated strings

I have this function in my program that converts integers to strings:

        QString Stats_Manager::convertInt(int num)
        {
            stringstream ss;
            ss &lt;&lt; num;
            return ss.str();
        }

But when ever i run this i get the error:

    aggregate &#39;std::stringstream ss&#39; has incomplete type and cannot be defined

Im not really sure what that means. But if you know how to fix it or need any more code please just comment. Thanks.


Content Type	Original Author	Original Content on Stackoverflow
Question	pighead10	View Question on Stackoverflow
Solution 1 - C++	Prasoon Saurav	View Answer on Stackoverflow
Solution 2 - C++	Yakov Galka	View Answer on Stackoverflow
Solution 3 - C++	rakslice	View Answer on Stackoverflow

Incomplete type is not allowed: stringstream

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

Will GetType() return the most derived type when called from the base class?

How does setTimeout work in Node.JS?

Attributions