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When should I use nil and NULL in Objective-C?
...ke a C pointer) in Objective-C. Like nil , NULL got no value nor address.
char *myChar = NULL;
struct MyStruct *dStruct = NULL;
So if there is a situation, when I need to check my struct (structure type variable) is empty or not then, I will use:
if (dStruct == NULL)
NSLog("The struct is emp...
(-2147483648> 0) returns true in C++?
...
@RichardJ.RossIII - with clang you are probably getting a 64-bit-typed literal, since it was too big to fit in an int. OP's implementation may not have a 64-bit type.
– Carl Norum
Feb 4 '1...
Difference between EXISTS and IN in SQL?
...way to avoid counting:
--this statement needs to check the entire table
select count(*) from [table] where ...
--this statement is true as soon as one match is found
exists ( select * from [table] where ... )
This is most useful where you have if conditional statements, as exists can be a lot ...
Specifically, what's dangerous about casting the result of malloc?
...f. Here's an example code fragment for discussion purposes.
main()
{
char * c = (char *)malloc(2) ;
printf("%p", c) ;
}
Suppose that the returned heap pointer is something bigger than what is representable in an int, say 0xAB00000000.
If malloc is not prototyped to return a pointer, the ...
jQuery to retrieve and set selected option value of html select element
I am attempting to retrieve and set the selected value of a select element (drop down list) with jQuery.
9 Answers
...
DISTINCT for only one column
...
If you are using SQL Server 2005 or above use this:
SELECT *
FROM (
SELECT ID,
Email,
ProductName,
ProductModel,
ROW_NUMBER() OVER(PARTITION BY Email ORDER BY ...
How do you implement a class in C? [closed]
...n(Object *self);
/// Person.h
typedef struct Person {
Object obj;
char *name;
} Person;
int Person_init(Person *self, char *name);
int Person_greet(Person *self);
int Person_clean(Person *self);
/// Object.c
#include "object.h"
int Object_init(Object *self)
{
self->uuid = uuid_new...
COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better? [duplicate]
...for all your queries that need to count everything, even for joins, use *
SELECT boss.boss_id, COUNT(subordinate.*)
FROM boss
LEFT JOIN subordinate on subordinate.boss_id = boss.boss_id
GROUP BY boss.id
But don't use COUNT(*) for LEFT joins, as that will return 1 even if the subordinate table doe...
When to use Common Table Expression (CTE)
...ing well? Can someone give me a simple example of limitations with regular select, derived or temp table queries to make the case of CTE? Any simple examples would be highly appreciated.
...
Which is fastest? SELECT SQL_CALC_FOUND_ROWS FROM `table`, or SELECT COUNT(*)
...irm this - I just updated a query with 4 joins on a 168,000 row database. Selecting just the first 100 rows with a SQL_CALC_FOUND_ROWS took over 20 seconds; using a separate COUNT(*) query took under 5 seconds (for both count + results queries).
– Sam Dufel
Ju...