*在c中是什么意思

Question

This is a C language question.

Does the * mean multiply or something else in function below? The reason I ask is because the function definition comments says it expects three params. Also do the () [parenthesis] in the #defines mean something different from no parenthesis? See below.

The function call:

nvm_eeprom_write_byte(TEST_ERASE_PAGE * EEPROM_PAGE_SIZE, 42);

The definitions:

#define TEST_ERASE_PAGE 2
#define EEPROM_PAGE_SIZE 32

Comments for the function definition:

• param page_addr EEPROM Page address, between 0 and EEPROM_SIZE/EEPROM_PAGE_SIZE.
• param byte_addr EEPROM Byte address, between 0 and EEPROM_PAGE_SIZE.
• param value Byte value to write to EEPROM.

The function definition:

void nvm_eeprom_write_byte(eeprom_addr_t address, uint8_t value) {}

eeprom_addr_t is a typedef:

typedef uint16_t eeprom_addr_t
#define EEPROM_START     (0x0000)
#define EEPROM_SIZE      (2048)
#define EEPROM_PAGE_SIZE (32)
#define EEPROM_END       (EEPROM_START + EEPROM_SIZE - 1)

Answer 1

Yes, it just means multiply in this context. It's multiplying two #defined constant to make the first argument to the nvm_eeprom_write_byte function.

This code involves a lot of assumptions about memory address manipulation. Gotta be honest with you, if you don't know C, looking at EEPROM driver code probably isn't the simplest or safest way to start.

Answer 2

Yes, * means multiply in C.

Parenthesis in #define is a standard practice in C to prevent unexpected results when using compound statements (where operator precedence matters).

Consider the difference between

#define FOO 1+2
int a = FOO*2

and

#define FOO (1+2)
int a = FOO*2