大约有 16,000 项符合查询结果（耗时：0.0280秒） [XML]
Can table columns with a Foreign Key be NULL?
...
Yes, you can enforce the constraint only when the value is not NULL. This can be easily tested with the following example:
CREATE DATABASE t;
USE t;
CREATE TABLE parent (id INT NOT NULL,
PRIMARY KEY (id)
) ENGINE=INNODB;
CREATE TABLE...
Round to 5 (or other number) in Python
...thon, but this works for me:
Python 2
def myround(x, base=5):
return int(base * round(float(x)/base))
Python3
def myround(x, base=5):
return base * round(x/base)
It is easy to see why the above works. You want to make sure that your number divided by 5 is an integer, correctly rounde...
What is the best way to find the users home directory in Java?
...\Application Data (CSIDL_LOCAL_APPDATA).
Sample JNA code:
public class PrintAppDataDir {
public static void main(String[] args) {
if (com.sun.jna.Platform.isWindows()) {
HWND hwndOwner = null;
int nFolder = Shell32.CSIDL_LOCAL_APPDATA;
HANDLE hToken...
Java: method to get position of a match in a String?
...
The family of methods that does this are:
int indexOf(String str)
indexOf(String str, int fromIndex)
int lastIndexOf(String str)
lastIndexOf(String str, int fromIndex)
Returns the index within this string of the first (or last) occurrence of the specified ...
What are some uses of template template parameters?
...he exact type explicitly.
which you can use like this:
f<std::vector, int>(v); // v is of type std::vector<int> using any allocator
or better yet, we can just use:
f(v); // everything is deduced, f can deal with a vector of any type!
UPDATE: Even this contrived example, while illu...
Access to the path is denied
...ile without set the file name.
Old Code
File.WriteAllBytes(@"E:\Folder", Convert.FromBase64String(Base64String));
Working Code
File.WriteAllBytes(@"E:\Folder\"+ fileName, Convert.FromBase64String(Base64String));
share
...
Getting View's coordinates relative to the root layout
...swers. One claims to be faster, and another claims to be easier.
private int getRelativeLeft(View myView) {
if (myView.getParent() == myView.getRootView())
return myView.getLeft();
else
return myView.getLeft() + getRelativeLeft((View) myView.getParent());
}
private int get...
What is the difference between UTF-8 and Unicode?
...his topic:
A chinese character: 汉
it's unicode value: U+6C49
convert 6C49 to binary: 01101100 01001001
Nothing magical so far, it's very simple. Now, let's say we decide to store this character on our hard drive. To do that, we need to store the character in binary format. We can s...
Android, ListView IllegalStateException: “The content of the adapter has changed but ListView did no
...hers to refer.
My loader on the main screen loads the phone book contacts into my data sources in the background.
@Override
public Void loadInBackground() {
Log.v(TAG, "Init loadings contacts");
synchronized (SingleTonProvider.getInstance()) {
PhoneBookManager.p...
Which, if any, C++ compilers do tail-recursion optimization?
... done for more than a decade), even for mutually recursive calls such as:
int bar(int, int);
int foo(int n, int acc) {
return (n == 0) ? acc : bar(n - 1, acc + 2);
}
int bar(int n, int acc) {
return (n == 0) ? acc : foo(n - 1, acc + 1);
}
Letting the compiler do the optimisation is stra...