C、C、Java 和 C# 中的前后递增运算符行为有何不同？

Pre and Post Increment Operator Behavior in C, C++, Java, and C#

This question explores the subtle nuances of pre and post increment operators in four different programming languages: C, C++, Java, and C#. The variations in their evaluations and side effects can lead to unexpected results.

C and C++

In C and C++, the order of subexpressions evaluation within an expression is unspecified. This means that statements containing multiple increment operators may not behave as expected. Additionally, modifying the same object twice within an expression without an intervening sequence point (such as a semicolon) constitutes undefined behavior.

Java and C#

In contrast, Java and C# evaluate expressions from left to right, ensuring that side effects are visible immediately. This behavior leads to more predictable results with pre and post increment operators.

Example

Consider the following code snippet:

int a = 2;
int b = a++ + a++;
int c = ++a + a++ + a++;

The output of this code in each language is as follows:

C	C++	Java	C#
7	7	7	7
4	4	5	5
15	15	16	16

The differences stem from the languages' evaluation strategies. In Java and C#, the left-to-right evaluation ensures consistent side effects, while in C/C++ the undefined behavior can lead to unpredictable outcomes.

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