从python转c++

C++ for Python Programmers

Adapted from a document by Rich Enbody & Bill Punch of Michigan State University

Purpose of this document

This document is a brief introduction to C++ for Python programmers -- something to

help start a transition to C++. It is not meant to be a complete introduction to C++.

Brevity took precedence over details.

Why C++?

Why should Python programmers care about C++?

powerful set of tools and will be your friend.

There are other languages worth learning, but this page is devoted solely to the transition

from Python to C++. Note that C++ preceded Java and C# so one finds many similarities

(as well as significant differences). Once one learns C++ it is relatively easy to transition

to the other two.

Finally, language choice need not be an "either/or" situation. You can code in Python and

then incorporate C++ where you need speed or low-level access to system components. It

is relatively easy to wrap C++ libraries for calling from Python (many useful ones are

already wrapped for you). Python plays well with other languages. Tools such as Bgen,

PySTL, and Sip help.

Kernighan and Ritchie began. Since C++ is derived from C, we'll start the traditional

way.

#include <iostream>

using namespace std;

int main()

{

cout << "Hello World!";

return 0;

}

The first thing a Python programmer notices is significant overhead to simply print a

beginning and end of a block of code, in this case the beginning and end of the function

main.

The statement cout << "Hello World!"; directs the string to cout, the standard

output stream, which displays it. Indentation is optional in C++, but code will be

unreadable, if you do not indent. If you indent like you were forced to do in Python, your

code will be readable.

Gotcha #1: Statements in C++ end with a semicolon ";" (that isn't precisely correct, but

will do for now).

Running the program.

C++ is a compiled language so you must compile it before executing it. Compilation

g++ hello.cpp

If compilation is successful, the executable code will by default be written to a file named

a.out which can be executed by simply typing a.out at the command prompt. If the

compiler finds syntactical errors in the program, error messages will be printed.

On a Windows computer the Visual C++ development environment is an excellent, but

sophisticated, way to create and run programs (named VisualStudio). You compile and

edit within the same application. Compilation is done by "building" the program.

Running is simply a command in the application.

C++ is strongly typed

C++ is a strongly typed language -- not precisely strongly typed, but close enough for

now. That is, all objects (things you name) must be declared before use. Python figures

(Don't worry the compiler will yell at you, if you forget.)

Note how each statement ends with a semicolon (Gotcha #1).

C++ types

Some C++ types are familiar:

• int

• float

• bool: same as Boolean

• string: may require #include<string>

Some are unfamiliar:

• char: single character, but a string of length one is not equivalent.

Assignment is familiar:

x = 4;

but, multi-assignment is not allowed: