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error: cannot dynamic_cast ‘b’ (of type ‘class Base*’) to type ‘c...
...以将析构函数设置为虚函数.
更正后的代码为(来自: c++ - converting a base class pointer to a derived class pointer)：
#include <iostream>
using namespace std;
class Base {
public:
Base() {};
virtual ~Base() {}; // make it polymorphic
};
template<class T>
class ...
jsonify a SQLAlchemy result set in Flask [duplicate]
...(inst, cls):
"""
Jsonify the sql alchemy query result.
"""
convert = dict()
# add your coversions for things like datetime's
# and what-not that aren't serializable.
d = dict()
for c in cls.__table__.columns:
v = getattr(inst, c.name)
if c.type in con...
What is the difference between static_cast and C style casting?
...o, static_cast conversion is not necessarily safe.
static_cast is used to convert from pointer to base class to pointer to derived class, or between native types, such as enum to int or float to int.
The user of static_cast must make sure that the conversion is safe.
The C-style cast does not pe...
php - get numeric index of associative array
...s happens?
Because when doing comparisons between strings and integers PHP converts strings to integers (and this is kinda stupid in my opinion), so when array_search() searches for the index it stops at the first one because apparently ("car" == 0) is true.
Setting array_search() to strict mode won...
How to get last inserted id?
... myCommand.Parameters.AddWithValue("@GameId", newGameId);
primaryKey = Convert.ToInt32(myCommand.ExecuteScalar());
myConnection.Close();
}
This will work.
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...
Context switches much slower in new linux kernels
...in your setup, just cat the current_driver file in the cpuidle section of /sys/devices/system/cpu as follows:
cat /sys/devices/system/cpu/cpuidle/current_driver
If you want your modern Linux OS to have the lowest context switch latency possible, add the following kernel boot parameters to disable...
How to get the number of Characters in a String?
...?"
???????????? alone is one grapheme, but, from unicode to code points converter, 4 runes:
????: women (1f469)
dark skin (1f3fe)
ZERO WIDTH JOINER (200d)
????red hair (1f9b0)
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byte + byte = int… why?
.../byte efficient instructions. Those that don't generally have a store-and-convert-to-signed-value-of-some-bit-length.
In other words, this decision must have been based on perception of what the byte type is for, not due to underlying inefficiencies of hardware.
...
Flatten nested dictionaries, compressing keys
... 6: 0,
7: 0}}}}}}}}}
import sys
sys.setrecursionlimit(1000000)
forget = lambda a,b:''
>>> time(lambda: dict(flattenDict(makeEvilDict(10000), join=forget)) )
took 0.10 seconds
>>> time(lambda: dict(flattenDict(makeEvilDict(100000), jo...
Hidden Features of C++? [closed]
...e type (i.e. no defaulted arguments) function1 and function2 are implictly converted to function pointers, and the result is implicitly converted back.
– MSalters
Nov 12 '10 at 15:49
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