Languages/C/SplitCH
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Source and header file split
It is sometimes complicated to split the header and the source file, here are some hints:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as deescribed in RFC 2119.
- (1) The header MUST contain what is necessary from the outside of the source file.
- (2) The header SHOULD NOT contain, what is not necessary.
- There is no reason to pollute the namespace of the whole project.
- Keeping the interface small and as clean as possible will make team work simpler.
- (3) The header file MUST prevent multiple inclusion, by using include guards.
- (4) A header file SHOULD be complete (it defines or includes all it needs).
- Example, if you use a uint32_t parameter in a function, the header should include <stdint.h>.
- (5) A header file SHOULD not include files only used in source file.
- (6) The header SHOULD be commented enough so there is no need to open the source file.
- (7) The source file MUST include the header, preferably first.
- This will ensure consistency and (4)
- (8) All symbols not exported by the header SHOULD be static (functions and variables).
- This will prevent namespace pollution
- Free benefit: the compiler can do better optimization (automatic inline, ...)
Temperature sensor example
Here is a small example, using main.c, temp_sensor.h, and temp_sensor.c
main.c
#include <stdio.h> #include "temp_sensor.h" int main(int argc, char *argv[]) { return printf("temperature is : %d", temp_sensor_get()); }
temp_sensor.h
/** * \file temp_sensor.h * * \brief Temperature sensor driver */ #ifndef TEMP_SENSOR_H // (3) prevent multiple inclusion, see the #endif at the end #define TEMP_SENSOR_H #include <stdint.h> // (4) We use stdint in the interface ! // (6) Full comments, no need to open temp_sensor.c // (1) This function is needed in main /** * \brief Get the temperature * * \return the temperature in K. * * \warning the value will be 0 if the sensor read fails. */ uint16_t temp_sensor_get(void); #endif /* TEMP_SENSOR_H */
temp_sensor.c
/** * \file temp_sensor.c * * \brief Temperature sensor driver implementation */ #include "temp_sensor.h" // (7) Include the header for compile-time checks #include <super_os/i2c.h> // (5) The i2c bus is not used in main, so it is included in this .c file, not in the .h // (2) These defines are private, we don't want to see them in main #define SENSOR_ADDRESS 0x12 #define SENSOR_REG 0x33 // (8) this function is not exported -> static // (6) this function MUST be commented here /** * \brief Do the real work here * \param chip, the i2c address of the chip * \param address, the address in the chip * \param value, where to store the value * \return 0 for no problem */ static uint8_t read(uint8_t chip, uint8_t address, uint16_t *value) { if (i2c_read(chip, address, value, 2) != 0) { return 0; } return 1; } // (6) This function is already commented in the header uint16_t temp_sensor_get(void) { uint16_t temp; uint8_t status = read(SENSOR_ADDRESS, SENSOR_REG, &temp); // Do what is said in temp_sensor.h if (status) { temp = 0; } return temp; }