union

Storing a uint64_t data type in a char type field present in a union in C

Hi I have the following union which is part of a larger struct and I want to store a uint64_t (64 bits size) data in this union. However i want to store it by accessing the id_data field since the others are not large enough for a complete uint64_t. But i dont know how to assign my uint64_t data into this id_data field. I know how to ...

Anonymous union within struct not in c99?

Hi, here is very simplified code of problem I have: enum node_type { t_int, t_double }; struct int_node { int value; }; struct double_node { double value; }; struct node { enum node_type type; union { struct int_node int_n; struct double_node double_n; }; }; int main(void) { struct int_no...

Using a union for multiple interpretations of IP address?

At work we have the following construct to enable interpreting an IP address as either an array of 4 bytes, or as a 32-bit integer: static const unsigned int IP_V4_LENGTH = 4; union IPv4Data { u_int32 address; u_int8 bytes[IP_V4_LENGTH]; }; This works fine, but I'm a little worried after reading chapter 97 "Don't use unions to...

Clever way to add the same parameter to mulitple locations in a prepared-statement

I have a JDBC query like select * from table1 where col1 between x and y union all select * from table2 where col1 between x and y union all select * from table3 where col1 between x and y I'm using a prepared-statement and am wondering if there is a cleverer way to set x and y without saying setDate(1, x);setDate(2, y);setDate(3, x);...

Accessing variables in a union inside a struct

Can anyone please explain why the 1st method of accessing a nested struct element inside an union in a struct works and the 2nd does not? typedef struct element Node; struct element { int type; union { int value; Node *child[2]; } u; }; int main() { Node n; Node *p; n.type = 0; p = n.u...

2 SQL Queries from same table

I am looking to grab the first row (ordered by date descending) from a table, and then grab the rest of the rows (ordered by last_name ascending). I'm assuming I need to use a UNION statement for this, but I'm having trouble getting it to work. Thanks in advance ...

Oracle: How do I grab a default value when a more specific value is null from within the same query?

That title is brutal, but I don't know how else to put it. I have a key value table tied to a user_id that stores user preferences throughout the site. If a user hasn't gone in and updated any of their settings, any time I ask for a key (say "FAVORITE_COLOR" it's going to be null, so I need to pull the default setting that I have tied ...

C++ "Choice" Union

Not sure if there is a term for this, "choice" seems to work. I'm working in C++, and I have a bunch of unions I need to create where the union represents a choice of one of the members of the union. The current "choice" is tracked and is always available. I am currently coding these "unions" manually, but I'm wondering whether there is ...

MySQL UNION with COUNT aliasing

I am trying to retrieve two counts from two separate tables into one SQL query to use with PHP. This is the current SQl query: SELECT COUNT(entryid) AS total FROM rh_entries UNION SELECT COUNT(pentryid) AS attended FROM rh_playerentries WHERE playerid=79 This is the PHP I am using to utilize the data: $result = mysql_query($query); $...

SQLite on Android: Union with limits alternative

I want to create a Cursor, which later I will pass via CursorAdapter to AutoCompleteTextView for autocompletion suggestions. The problem is that my SQL statement needs to select 2 different result sets from the same table, just sorted by different criteria. At the same time these result sets must not overlap - otherwise I would have mult...

Populate Typed Dataset wit UNION ALL SQL query

I have a strange situation here and I hope someone can help me. I don't have the same problem when using an untyped dataset. OK. I have a typed dataset MyDS with a typed datatable MyTable (TableID, Title, Message). The table gets filled with results from two tables, using a UNION ALL Select TableAID, TableATitle, Message FROM T...

What are the semantics of unions with both volatile and nonvolatile members?

More specifically, I have (simplified) the following: union foo { volatile int bits; char data[sizeof(int)*CHAR_BIT]; } If I never access the first sizeof(int) items of data, can i rely on bits working as expected? ...

SQL select until full sort of problem

Hi I am trying to write some SQL that pulls from several tables using unions, where the date on the rows is less than a hour. But if the total rows from the SQL query doesn't add up to about 20 then it should change the where to the date being less than two hours and so forth until 20 rows retrieved. Is this possible to do solely in S...

Advantages of using union when same thing can be done using struct - C

I have difficulty in understanding the use of union in C. I have read lot of posts here on SO about the subject. But none of them explains about why union is preferred when same thing can be achieved using a struct. Quoting from K&R As an example such as might be found in a compiler symbol table manager, suppose that a constant...

Structures and Unions in C, determining size and accessing members

All, Here is an example on Unions which I find confusing. struct s1 { int a; char b; union { struct { char *c; long d; } long e; }var; }; Considering that char is 1 byte, int is 2 bytes and long is 4 bytes. What would be the size of the entire struct here ? Will the...

Are PostgreSQL VIEWS created newly each time they are queried against?

I am creating a web app which has some complex underlying associations. In order to solve several issues I was having I created a UNION View. There are probably a lot of other ways this could be solved. But I am now considering the efficiency of my design, and I wanted to know if a VIEW is newly created each time it is queried, or is it...

Shortening a repetitive 1400-line MySQL UNION query using PHP

I have a MYSQL table that is 1275 fields wide. Each row in the table represents a single class of students, with 17 fields per student, X up to 75 students per class, so 17 X 75 = 1275 fields. I have devised an SQL UNION query that successfully pulls the students into another table, with each student on a single row. Now, I want t...

union consisting of float : completely insane output

#include <stdio.h> union NumericType { float value; int intvalue; }Values; int main() { Values.value = 1094795585.00; printf("%f \n",Values.value); return 0; } This program outputs as : 1094795648.000000 Can anybody explain Why is this happening? Why did the value of the float Values.value increase? Or am I m...

SQL Union/Join Query

I have a user profile table with columns User Name, manager and many other fields, for example amount.. Example Records:- User Manager Amount A B 100 x y 200 B C 300 M N 800 C D 500 P Q 1000 D E 1000 I am trying to get the result as below:- User...

ANSI C unions - are they really useful?

From a response to some question yesterday, I learned that it is nonportable and unsafe to write into one union member and read the value from another member of a different type, assuming underlying alignment of the members. So after some research I found a written source that repeats this claim and specifies a popular example - using un...