大约有 1,645 项符合查询结果（耗时：0.0121秒） [XML]
Why it's not possible to use regex to parse HTML/XML: a formal explanation in layman's terms
... or bonbon. Matching of recursive/balanced structures make these even more fun.
Wikipedia puts this nicely, in a quote by Larry Wall:
'Regular expressions' [...] are only marginally related to real regular expressions. Nevertheless, the term has grown with the capabilities of our pattern matchi...
How to sort in-place using the merge sort algorithm?
...he rest as working area for merging.
For example like the following merge function.
void wmerge(Key* xs, int i, int m, int j, int n, int w) {
while (i < m && j < n)
swap(xs, w++, xs[i] < xs[j] ? i++ : j++);
while (i < m)
swap(xs, w++, i++);
while (...
Adding new column to existing DataFrame in Python pandas
...)
As per this example (which also includes the source code of the assign function), you can also include more than one column:
df = pd.DataFrame({'a': [1, 2], 'b': [3, 4]})
>>> df.assign(mean_a=df.a.mean(), mean_b=df.b.mean())
a b mean_a mean_b
0 1 3 1.5 3.5
1 2 4 1...
Null vs. False vs. 0 in PHP
...ill get inequality.
So why are they useful ?
Well, look at the strrpos() function. It returns False if it did not found anything, but 0 if it has found something at the beginning of the string !
<?php
// pitfall :
if (strrpos("Hello World", "Hello")) {
// never exectuted
}
// smart move ...
Insert, on duplicate update in PostgreSQL?
...RT, as appropriate:
CREATE TABLE db (a INT PRIMARY KEY, b TEXT);
CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
$$
BEGIN
LOOP
-- first try to update the key
-- note that "a" must be unique
UPDATE db SET b = data WHERE a = key;
IF found THEN
...
Why do we need message brokers like RabbitMQ over a database like PostgreSQL?
...em) on top of a database. I can tell you that it is possible, but it's not fun and it doesn't usually pay off to do it. Some of the problems you mention can be worked around, but it does increase the complexity quite a lot. All in all I agree: use a dedicated MQ system, if you need one. For low work...
Why not infer template parameter from constructor?
... infer template parameters from class constructors, much as it can do from function parameters? For example, why couldn't the following code be valid:
...
Code Golf - π day
...
@Load: 5.1.2.2.1/1: The function called at program startup is named main. It shall be defined … or in some other implementation-defined manner. So that's because the implementation can accept this form.
– kennytm
...
Find XOR of all numbers in a given range
...s the fact that there is a pattern of results in the running XORs. The f() function calculates the XOR total run from [0, a]. Take a look at this table for 4-bit numbers:
0000 <- 0 [a]
0001 <- 1 [1]
0010 <- 3 [a+1]
0011 <- 0 [0]
0100 <- 4 [a]
0101 <- 1 [1]
0110 <- 7 [a+1...
Is there a better way to express nested namespaces in C++ within the header
...races that were missing comments about which brace closes which scope? Not fun.).
MY_COMPANY_BEGIN
MY_LIBRARY_BEGIN
class X { };
class Y { };
MY_LIBRARY_END
MY_COMPANY_END
If you want to put all namespace declarations on a single line you can do that as well with a bit of (pretty ugly) preproc...