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undefined reference to boost::system::system_category() when compiling
...
The boost library you are using depends on the boost_system library. (Not all of them do.)
Assuming you use gcc, try adding -lboost_system to your compiler command line in order to link against that library.
...
Fastest way to list all primes below N
...on.
Below is a script which compares a number of implementations:
ambi_sieve_plain,
rwh_primes,
rwh_primes1,
rwh_primes2,
sieveOfAtkin,
sieveOfEratosthenes,
sundaram3,
sieve_wheel_30,
ambi_sieve (requires numpy)
primesfrom3to (requires numpy)
primesfrom2to (requires numpy)
Many thanks to...
How well is Unicode supported in C++11?
... what std::string and its siblings should do:
The class template basic_string describes objects that can store a sequence consisting of a varying number of arbitrary char-like objects with the first element of the sequence at position zero.
Well, std::string does that just fine. Does that pro...
Difference between reduce and foldLeft/fold in functional programming (particularly Scala and Scala
...ase of foldLeft
scala> val intParList: ParSeq[Int] = (1 to 100000).map(_ => scala.util.Random.nextInt()).par
scala> timeMany(1000, intParList.reduce(_ + _))
Took 462.395867 milli seconds
scala> timeMany(1000, intParList.foldLeft(0)(_ + _))
Took 2589.363031 milli seconds
reduce vs fo...
How can I select and upload multiple files with HTML and PHP, using HTTP POST?
...nctype="multipart/form-data">
<input type="file" name="my_file[]" multiple>
<input type="submit" value="Upload">
</form>
<?php
if (isset($_FILES['my_file'])) {
$myFile = $_FILES['my_file'];
$f...
Find the nth occurrence of substring in a string
... more Pythonic version of the straightforward iterative solution:
def find_nth(haystack, needle, n):
start = haystack.find(needle)
while start >= 0 and n > 1:
start = haystack.find(needle, start+len(needle))
n -= 1
return start
Example:
>>> find_nth("fo...
Trying to login to RDP using AS3
...ion sendMcsData(): ByteArray {
trace("Secure.sendMcsData");
var num_channels: int = 2;
var dataBuffer:ByteArray=new ByteArray(); //RdpPacket_Localised dataBuffer = new RdpPacket_Localised(512);
// it's better to build the data buffer in the function, as in java, otherwise you can rec...
Printf width specifier to maintain precision of floating-point value
...be to print one seventh as in:
#include <float.h>
int Digs = DECIMAL_DIG;
double OneSeventh = 1.0/7.0;
printf("%.*e\n", Digs, OneSeventh);
// 1.428571428571428492127e-01
But let's dig deeper ...
Mathematically, the answer is "0.142857 142857 142857 ...", but we are using finite precision...
Finding the index of an item in a list
...atch, you can give index a hint. For instance, in this snippet, l.index(999_999, 999_990, 1_000_000) is roughly five orders of magnitude faster than straight l.index(999_999), because the former only has to search 10 entries, while the latter searches a million:
>>> import timeit
>>&g...
Is cout synchronized/thread-safe?
... @ildjarn - No, @edA-qa mort-ora-y is correct. As long as cout.sync_with_stdio() is true, using cout to output characters from multiple threads without additional synchronization is well-defined, but only on the level of individual bytes. Thus, cout << "ab"; and cout << "cd" exec...