Databases
StackOverflow2013
Postsdbo
POHow to work with null pointers in a std::vector
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow to work with null pointers in a std::vector
    primarykey
    data
    text
    <p>Say I have a vector of null terminates strings some of which may be null pointers. I don't know even if this is legal. It is a learning exercise.<br> Example code<br></p> <pre><code>std::vector&lt;char*&gt; c_strings1; char* p1 = "Stack Over Flow"; c_strings1.push_back(p1); p1 = NULL; // I am puzzled you can do this and what exactly is stored at this memory location c_strings1.push_back(p1); p1 = "Answer"; c_strings1.push_back(p1); for(std::vector&lt;char*&gt;::size_type i = 0; i &lt; c_strings1.size(); ++i) { if( c_strings1[i] != 0 ) { cout &lt;&lt; c_strings1[i] &lt;&lt; endl; } } </code></pre> <p>Note that the size of vector is 3 even though I have a NULL at location <code>c_strings1[1]</code><br> <strong>Question</strong>. How can you re-write this code using <code>std::vector&lt;char&gt;</code> What exactly is stored in the vector when you push a null value? <br><br> <strong>EDIT</strong><br> The first part of my question has been thoroughly answered but not the second. Not to my statisfaction at least. I <strong>do</strong> want to see usage of <code>vector&lt;char&gt;</code>; not some nested variant or <code>std::vector&lt;std::string&gt;</code> Those are familiar. So here is what I tried ( hint: it does not work) <br></p> <pre><code>std::vector&lt;char&gt; c_strings2; string s = "Stack Over Flow"; c_strings2.insert(c_strings2.end(), s.begin(), s.end() ); // char* p = NULL; s = ""; // this is not really NULL, But would want a NULL here c_strings2.insert(c_strings2.end(), s.begin(), s.end() ); s = "Answer"; c_strings2.insert(c_strings2.end(), s.begin(), s.end() ); const char *cs = &amp;c_strings2[0]; while (cs &lt;= &amp;c_strings2[2]) { std::cout &lt;&lt; cs &lt;&lt; "\n"; cs += std::strlen(cs) + 1; } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USuser841550
    1. USuser841550
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow to work with null pointers in a std::vector
      1. This table or related slice is empty.
      1. VTUpMod
    1. COJust don't use C-strings in C++. If you used `std::string` I think these questions would just go away.
      singulars
      1. POHow to work with null pointers in a std::vector
      1. USMark B
    2. COYou're a bit confused because of "null terminated strings, some of which may be null pointers". A null-terminated string is an array of characters, the last one of which is 0. The null pointer doesn't point to anything. Therefore the null pointer doesn't point to a null-terminated string either. So your vector contains a mix of null-terminated strings and null pointers.
      singulars
      1. POHow to work with null pointers in a std::vector
      1. USMSalters
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload