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Uniform Initialization
Multithreading
Smart Pointers
Hash Tables
std::array Container
Move Semantics
Lambdas
Type Inference in C++ (auto and decltype)
Initializers in if and switch Statements
Introduction
Syntax
Summary
Standard Template Library (STL) on Concurrent and Parallel Algorithms
Nested Namespaces
Introduction to SYCL Essentials
Module 1: oneAPI Intro
Module 2: DPCPP Program Structure
Module 3: DPCPP Unified Shared Memory
Module 4: DPCPP Sub-Groups
Module 5: Intel® Advisor
Module 6: VTune™ Profiler
Module 7: DPCPP Library
Module 8: DPCPP Reduction
Module 9: DPCPP Buffers And Accessors In Depth
Module 10: DPCPP Graphs Scheduling Data Management
Module 11: Intel® Distribution for GDB
Module 12: DPCPP Local Memory And Atomics
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Initializers in if and switch Statements
This chapter covers initializer statements in if and switch blocks. You will learn the following:
What is an initializer statement?
How can you benefit from using it inside the if-else and switch blocks?
What is the syntax of initializer statements in if and switch blocks?
Introduction
There are many situations when we need to check the value returned by a function or perform conditional operations based on the value of the function. Let's look at the example pseudocode below:
// some function declaration
int foo(/*...*/)
// function call and return value storing in variable
int var = foo(/*...*/);
if (var == /*some value*/){
// do something
} else {
// do something else
}There is nothing wrong with this code, but it can be improved in certain situations. As shown in the example, the variable var is used only for this if-else statement. At the same time, it leaks into the surrounding scope. In that case, we need to make sure to not mix it up with other variables. Also, if the compiler can explicitly know that this variable will only be used there, it may potentially produce more optimized code.
Syntax
Let's look at the syntax of the if-else and switch blocks.
Initializer Statement Outside the Conditional Blocks
You may notice that if-else conditional blocks and switch blocks have a generic format. First, we have an initialization of a variable that will be checked, and then there is a conditional block using this initialized variable. For an if-else block, it usually looks like this:
// initializer-statement
if (condition){
// do something
} else {
// do something else
}And for switch block, similarly, like this:
// initializer-statement
switch(variable){
// cases
}Initializer Statements in if and switch Blocks
Starting with C++17, it is possible to initialize a variable inside if and switch statements:
if (initializer-statement; condition){
// do something
} else {
// do something else
}switch(initializer-statement; variable){
// cases
}Summary
Initializers in if and switch statements allow the variable to be assigned to the scope of this statement. Note that using this language feature can result in more complex code when initialization and comparison are separate concerns.