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Is std::unique_ptr required to know the full definition of T?
...s. However shared_ptr and unique_ptr are partial exceptions. Some, but not all of their members can be instantiated with incomplete types. The motivation for this is to support idioms such as pimpl using smart pointers, and without risking undefined behavior.
Undefined behavior can occur when you h...
Does anyone have benchmarks (code & results) comparing performance of Android apps written in Xamari
...y to stay inside the Mono VM most of the time, we do not know how Mono actually accesses the disk.
It is also telling that our C# code uses SQLite.NET (https://github.com/praeclarum/sqlite-net). Identical fetches using the SQLite.NET code are also 2x slower than using Android's Java SQLite wrapper....
Git Bash doesn't see my PATH
...ecutable names without extensions. In my case, I wanted to execute a file called cup.bat. In a Windows shell, typing cup would be enough. Bash doesn't work this way, it wants the full name. Typing cup.bat solved the problem. (I wasn't able to run the file though, since apparently bash couldn't under...
Is it possible to rotate a drawable in the xml description?
..."
android:pivotY="50%"
android:drawable="@drawable/mainmenu_background">
</rotate>
The fromDegrees is important.
Basically this is a rotate animation defined in XML. With fromDegrees you define the initial rotated state. The toDegrees is the final rotated state of the dra...
fstream默认不支持中文路径和输出整数带逗号的解决办法 - C/C++ - 清泛网 -...
... i << "/n"; //输出带逗号
outfile.close();
setlocale( LC_ALL, "C" ); //恢复全局locale，如果不恢复，可能导致cout无法输出中文
}
创建文件成功，在程序的“测试”文件下出现个test.txt文件。需要注意的是最后需要调用setlocale( ...
MySQL和MongoDB设计实例进行对比 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...查询：
db.getCollection("mobiles").find({
"params": {
$all: [
{$elemMatch: {"name": "待机时间", "value": {$gt: 100}}},
{$elemMatch: {"name": "外观设计", "value": "直板"}}
]
}
});
注：查询中用到的$all，$elemMatch等高...
Linux MySql编译安装 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...d mysql
useradd -g mysql mysql
#开始编译安装
cmake -DCMAKE_INSTALL_PREFIX=/usr/local/mysql \
-DMYSQL_UNIX_ADDR=/tmp/mysql.sock \
-DDEFAULT_CHARSET=utf8 \
-DDEFAULT_COLLATION=utf8_general_ci \
-DWITH_EXTRA_CHARSETS=all \
-DWITH_MYISAM_STORAGE_ENGINE=1 \
-DWITH_INNOBASE_STORAGE_ENGIN...
Why do you use typedef when declaring an enum in C++?
...
In C, declaring your enum the first way allows you to use it like so:
TokenType my_type;
If you use the second style, you'll be forced to declare your variable like this:
enum TokenType my_type;
As mentioned by others, this doesn't make a difference in C++. M...
Computed / calculated / virtual / derived columns in PostgreSQL
...(Not in Postgres 13, yet) .
Related:
Attribute notation for function call gives error
Until then, you can emulate VIRTUAL generated columns with a function using attribute notation (tbl.col) that looks and works much like a virtual generated column. That's a bit of a syntax oddity which exi...
Default value in Go's method
...s on the subject, but here are some specific examples.
**Option 1:** The caller chooses to use default values
// Both parameters are optional, use empty string for default value
func Concat1(a string, b int) string {
if a == "" {
a = "default-a"
}
if b == 0 {
b = 5
}
return fmt.S...