大约有 40,000 项符合查询结果（耗时：0.0579秒） [XML]
When should I use a composite index?
...olumn_A )
But it will not (at least not directly, maybe it can help partially if there are no better indices) help for queries that need
index( column_A, column_C )
Notice how column_B is missing.
In your original example, a composite index for two dimensions will mostly benefit queries that q...
Getting current unixtimestamp using Moment.js
I want to get the Unix TimeStamp using Moment.js.
I can find many functions which convert timestamp to date in moment.js.
I know that I can easily get the unix timestamp by using the following JavaScript function: Math.floor(new Date().getTime()/1000) .
...
input() error - NameError: name '…' is not defined
...
input function in Python 2.7, evaluates whatever your enter, as a Python expression. If you simply want to read strings, then use raw_input function in Python 2.7, which will not evaluate the read strings.
If you are using Python 3.x, raw_input has been renamed to input. Quoting the Python 3.0 rel...
What is the performance cost of having a virtual method in a C++ class?
...3ghz in-order PowerPC processor. On that architecture, a virtual function call costs 7 nanoseconds longer than a direct (non-virtual) function call.
So, not really worth worrying about the cost unless the function is something like a trivial Get()/Set() accessor, in which anything other than inli...
Distinct by property of class with LINQ [duplicate]
...
I think that no Overhead exists!
– Amirhossein Mehrvarzi
Dec 23 '13 at 13:47
6
...
What is a “callback” in C and how are they implemented?
...y're implemented using function pointers. Here's an example:
void populate_array(int *array, size_t arraySize, int (*getNextValue)(void))
{
for (size_t i=0; i<arraySize; i++)
array[i] = getNextValue();
}
int getNextRandomValue(void)
{
return rand();
}
int main(void)
{
int m...
Try-catch speeding up my code?
...eration on the loads and stores of the locals.
For some reason unclear to all of us, the problematic code generation path is avoided when the JITter knows that the block is in a try-protected region.
This is pretty weird. We'll follow up with the JITter team and see whether we can get a bug enter...
Can't install RMagick 2.13.1. Can't find MagickWand.h.
When I try do install rmagick I get the following error message:
32 Answers
32
...
Seeding the random number generator in Javascript
...nswered Feb 6 '09 at 17:42
PeterAllenWebbPeterAllenWebb
9,24833 gold badges3434 silver badges4444 bronze badges
...
Usage of sys.stdout.flush() method
... the data "written" to standard out before it writes it to the terminal). Calling sys.stdout.flush() forces it to "flush" the buffer, meaning that it will write everything in the buffer to the terminal, even if normally it would wait before doing so.
Here's some good information about (un)buffere...