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“hello, world” 起源及其他 - 创意 - 清泛网 - 专注C/C++及内核技术
“hello, world” 起源及其他学过编程语言的人都笑了，在程序员心目中，hello world是一切的开始，程序语言教科书的第一个演示程序、WordPress的第一篇示例文章（我的hello world）、环境搭建成功后的第一个测试…
问题的提出
相传...
How to concatenate string variables in Bash
...
foo="Hello"
foo="${foo} World"
echo "${foo}"
> Hello World
In general to concatenate two variables you can just write them one after another:
a='Hello'
b='World'
c="${a} ${b}"
echo "${c}"
> Hello World
...
Javascript call() & apply() vs bind()?
...cutes the function immediately:
var person = {
name: "James Smith",
hello: function(thing) {
console.log(this.name + " says hello " + thing);
}
}
person.hello("world"); // output: "James Smith says hello world"
person.hello.call({ name: "Jim Smith" }, "world"); // output: "Jim Smith s...
How to check if a Unix .tar.gz file is a valid file without uncompressing?
...mple of failed tar ball test...
$ echo "this will not pass the test" > hello.tgz
$ tar -xvzf hello.tgz -O > /dev/null
gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error exit delayed from previous errors
$ rm hello.*
Working Example...
$ ls hello*
ls: hello*: No such fi...
Assign multiple columns using := in data.table, by group
...t!
x <- data.table(a = 1:3, b = 1:6)
f <- function(x) {list("hi", "hello")}
x[ , c("col1", "col2") := f(), by = a][]
# a b col1 col2
# 1: 1 1 hi hello
# 2: 2 2 hi hello
# 3: 3 3 hi hello
# 4: 1 4 hi hello
# 5: 2 5 hi hello
# 6: 3 6 hi hello
x[ , c("mean", "sum") := list(mea...
How to pass parameters in $ajax POST?
... url as parameters, but if I set them directly to the url using /?field1="hello" it works.
9 Answers
...
OS detecting makefile
...d on five files
├── lib
│ └── Makefile
│ └── hello.h
│ └── hello.c
└── app
└── Makefile
└── main.c
Reminder: Makefile is indented using tabulation. Caution when copy-pasting below sample files.
The two Makefile files
1. lib/Ma...
What does the 'static' keyword do in a class?
...ce members. In the example given, main does not know which instance of the Hello class (and therefore which instance of the Clock class) it should refer to. static members can only refer to static members. Instance members can, of course access static members.
Side note: Of course, static members c...
What is the purpose of .PHONY in a Makefile?
...a directory 'test' following files are present:
prerit@vvdn105:~/test$ ls
hello hello.c makefile
In makefile a rule is defined as follows:
hello:hello.c
cc hello.c -o hello
Now assume that file 'hello' is a text file containing some data, which was created after 'hello.c' file. So the mo...
How do I use grep to search the current directory for all files having the a string “hello” yet disp
... search the current directory for any and all files containing the string "hello" and display only .h and .cc files?
8 Answ...