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In Docker, what's the difference between a container and an image? [duplicate]
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An image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. Images are read-only.
https://docs.docker.com/glossary/?term=image
A container is an active (or ...
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Converting bool to text in C++
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This is a defensive programming technique that protects against hidden order-of-operations errors; i.e., how does this evaluate for all compilers?
1 == 2 ? "true" : "false"
compared to
(1 == 2) ? "true" : "false"
s...
Java's Interface and Haskell's type class: differences and similarities?
...> so that the compareTo(T otherobject) kind of has type t -> t -> Ordering. But that still requires the programmer to follow this rule, and also causes headaches when people want to make a function that uses this interface, they have to have recursive generic type parameters.
Also, you won...
PostgreSQL error 'Could not connect to server: No such file or directory'
...un rake db:migrate in my project or even try most database tasks for my Ruby on Rails 3.2 applications.
22 Answers
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How do you unit test private methods?
...etimes like to call private methods from test methods. Most of the time in order to prevent code duplication for test data generation...
Microsoft provides two mechanisms for this:
Accessors
Goto the class definition's source code
Right-click on the name of the class
Choose "Create Private Acces...
C++ Build Systems - What to use? [closed]
...rams in a folder (i.e. .tup/mnt/@tupjob-XXXXX) as the working directory in order to monitor reads/writes, enforcing the build configuration. It works well, unless the path is stored absolutely (i.e. with symbols). When you compile a binary, the symbol path is stored in the binary itself. That means ...
Change one value based on another value in pandas
...we are adding a new description column as a concatenation of other columns by using the + operation which is overridden for series. Fancy string formatting, f-strings etc won't work here since the + applies to scalars and not 'primitive' values:
df['description'] = 'A ' + df.age.astype(str) + ' yea...
How to drop SQL default constraint without knowing its name?
....object_id INNER JOIN
sys.schemas s ON t.schema_id = s.schema_id
ORDER BY T.name, c.name
open table_names
fetch next from table_names into @table_name , @column_name
while @@fetch_status = 0
BEGIN
if exists (SELECT top(1) d.name from sys.tables t join sys.default_constraints d on d....
PostgreSQL create table if not exists
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CREATE TABLE myschema.mytable (i integer);
END IF;
END
$func$;
Call:
SELECT create_mytable(); -- call as many times as you want.
Notes:
The columns schemaname and tablename in pg_tables are case-sensitive. If you double-quote identifiers in the CREATE TABLE statement, you need ...