The meaning of register in c language

In C language, the register keyword prompts the compiler to store variables in CPU registers to improve access speed. It is suitable for frequently accessed small variables (such as integers or floating point types) whose scope is limited to one function. Although the compiler ultimately decides whether to store variables in registers, register can speed up access to local variables and reduce the number of memory accesses. When using it, consider register limit limits, avoid using it for large variables or shared variables, and enable compiler optimization options to support register allocation.

The meaning of register in C language

In C language, the register keyword is used to prompt the compiler Stores the given variable in the CPU's registers instead of in memory. This can significantly speed up access to the variable.

When to use register

• When the variable is accessed frequently.
• When the variable is small and can be placed in a register (usually an integer or floating-point variable).
• When the variable is a local variable and its scope is limited to a function.

How to use register

Just use the register keyword before the variable declaration. For example:

<code class="c">register int count;</code>

Advantages and disadvantages

Advantages:

• Improve variable access speed
• Reduce the number of memory accesses and reduce cache miss rate

Disadvantages:

• The number of registers is limited and may compete with other variables
• Tips that the compiler does not guarantee that the variable will be stored in the register, which ultimately depends on the compiler's optimization strategy
• If the variable exceeds the size of the register, it may cause performance degradation

Best Practice

• Mark only frequently accessed local variables as register.
• Avoid marking large variables or variables that may be shared between multiple functions as register.
• Use compiler optimization options such as -O2 or -O3 to enable register allocation optimization.

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