C_142 Types of Storage Classes in C - part 2 | register storage class

Summary

In this video, the instructor explains the concept of the register storage class in C programming, comparing it with the auto storage class. Key points include how variables declared with the register keyword are stored in CPU registers for faster access, improving program efficiency. The video also discusses the limitations, such as the inability to use global declarations with register variables, and the constraints of CPU register size. Additionally, the instructor addresses a common question about auto storage class behavior and guides viewers through a practical example to understand the register storage class more clearly.

Takeaways

• 😀 The main topic of the video is explaining the register storage class in C programming, specifically comparing it to the auto storage class.
• 😀 Register storage class is similar to the auto storage class, but with two main differences: the keyword used is 'register' and the variable is stored in CPU registers.
• 😀 The default value of a register variable is garbage value, similar to an auto variable, and its scope is limited to the block (function or method) in which it's declared.
• 😀 Register variables cannot be declared globally, similar to auto variables, and their lifetime lasts until the end of the block or function.
• 😀 The key difference between register and auto storage classes is the location where the variable is stored: auto variables are stored in RAM (stack), while register variables are stored in CPU registers.
• 😀 Storing variables in CPU registers allows for faster access and processing, which can improve program efficiency and reduce running time.
• 😀 Using register storage class for frequently accessed variables, such as loop counters or sum variables, can enhance program performance.
• 😀 Not all variables can be stored in CPU registers because registers have limited capacity, and storing too many variables could lead to memory issues.
• 😀 Declaring all variables as register is not practical due to the limited size of CPU registers. Only variables that are used frequently should be stored in registers.
• 😀 It is not guaranteed that variables declared with the register keyword will be stored in CPU registers; this depends on factors such as register availability and compiler behavior.
• 😀 You cannot use pointers with register variables because they do not have a specific memory address, making it impossible to take their address or dereference them.

Q & A

What is the main topic discussed in this video?

The main topic discussed is the 'register' storage class in C programming, focusing on its differences and usage compared to the 'auto' storage class.

What is the primary difference between the 'register' and 'auto' storage classes?

The primary difference is that the 'register' storage class stores variables in CPU registers for faster access, while 'auto' stores variables in RAM. Additionally, 'register' uses the 'register' keyword, and both storage classes are for local variables only.

Can we use the 'register' storage class for global variables?

No, the 'register' storage class is not allowed for global variables. It can only be used for local variables inside a function or block.

What is the default value of a variable declared with the 'register' storage class?

The default value of a variable declared with the 'register' storage class is a garbage value, similar to the 'auto' storage class.

Where are variables declared with the 'register' storage class stored?

Variables declared with the 'register' storage class are stored in CPU registers, which are faster than RAM for accessing data.

Why can't all variables be declared with the 'register' storage class?

Not all variables can be declared with the 'register' storage class because CPU registers have limited space. Storing too many variables in registers would result in insufficient memory for processing instructions.

What types of variables are most suitable for the 'register' storage class?

Variables that are frequently used or accessed, such as loop counter variables, are most suitable for the 'register' storage class. These variables benefit from faster access times.

What is a potential issue with using the 'register' storage class?

A potential issue is that it is not guaranteed that a variable will be stored in the CPU register, as it depends on factors like the availability of registers or the compiler's behavior.

Can you use pointers with variables declared as 'register'?

No, you cannot use pointers with variables declared as 'register' because these variables do not have a memory address in RAM, making it impossible to obtain their address.

What is the benefit of using the 'register' storage class in a program?

The benefit of using the 'register' storage class is that it allows faster access to frequently used variables by storing them in CPU registers, which can improve the program's performance by reducing access time to variables.