Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The common idiom is using both: </p> <pre><code>typedef struct X { int x; } X; </code></pre> <p>They are different definitions. To make the discussion clearer I will split the sentence:</p> <pre><code>struct S { int x; }; typedef struct S S; </code></pre> <p>In the first line you are defining the identifier <code>S</code> within the struct name space (not in the C++ sense). You can use it and define variables or function arguments of the newly defined type by defining the type of the argument as <code>struct S</code>:</p> <pre><code>void f( struct S argument ); // struct is required here </code></pre> <p>The second line adds a type alias <code>S</code> in the global name space and thus allows you to just write:</p> <pre><code>void f( S argument ); // struct keyword no longer needed </code></pre> <p>Note that since both identifier name spaces are different, defining <code>S</code> both in the structs and global spaces is not an error, as it is not redefining the same identifier, but rather creating a different identifier in a different place.</p> <p>To make the difference clearer:</p> <pre><code>typedef struct S { int x; } T; void S() { } // correct //void T() {} // error: symbol T already defined as an alias to 'struct S' </code></pre> <p>You can define a function with the same name of the struct as the identifiers are kept in different spaces, but you cannot define a function with the same name as a <code>typedef</code> as those identifiers collide.</p> <p>In C++, it is slightly different as the rules to locate a symbol have changed subtly. C++ still keeps the two different identifier spaces, but unlike in C, when you only define the symbol within the class identifier space, you are not required to provide the struct/class keyword:</p> <pre><code> // C++ struct S { int x; }; // S defined as a class void f( S a ); // correct: struct is optional </code></pre> <p>What changes are the search rules, not where the identifiers are defined. The compiler will search the global identifier table and after <code>S</code> has not been found it will search for <code>S</code> within the class identifiers.</p> <p>The code presented before behaves in the same way:</p> <pre><code>typedef struct S { int x; } T; void S() {} // correct [*] //void T() {} // error: symbol T already defined as an alias to 'struct S' </code></pre> <p>After the definition of the <code>S</code> function in the second line, the struct S cannot be resolved automatically by the compiler, and to create an object or define an argument of that type you must fall back to including the <code>struct</code> keyword:</p> <pre><code>// previous code here... int main() { S(); struct S s; } </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POtypedef struct vs struct definitions
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USDavid Rodríguez - dribeas
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POtypedef struct vs struct definitions
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COGreat answer shows me also why I want to typedef, so it can't be overwritten as a function, thanks : )
      singulars
      1. PO
      1. USAlexander Varwijk
    2. CO@AlexanderVarwijk: You want to `typedef` to avoid the need to qualify with `struct` or `enum`. If the naming conventions you use allow for a function and a type by the same name, the best you can do is review how you name the elements of your program.
      singulars
      1. PO
      1. USDavid Rodríguez - dribeas
    3. COMy naming conventions should make sure that doesn't happen, better safe than sorry though : )
      singulars
      1. PO
      1. USAlexander Varwijk
 

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