How am I supposed to declare this C++ function? - c++

Question

I have a C++ program with an undefined reference error on the call of a method in a class. As near as I can tell, the method is public and I'm calling it with a parameter declared the same as the method definition, but eclipse/gcc tells me it is undefined. I'm not used to C++, can someone please tell me what's wrong with the definition?
The main class:
#include <iostream>
using namespace std;
#include "AttenuationConfigurationTable.h"
int main()
{
flash_entry_struct flash_array[] = { { 10, 20, 30, 40 }, { 50, 60, 70, 80 }, { -1, -1, -1, -1 } };
// note: no undefined reference or any other error for the line with the class
AttenuationConfigurationTable attConfigTable;
// error appears for next line: undefined reference to ...load_attenuation_...
attConfigTable.load_attenuation_calibration_table_from_flash(flash_array);
return 0;
}
The class file:
#include "AttenuationConfigurationTable.h"
#include "flashEntryStruct.h"
AttenuationConfigurationTable::AttenuationConfigurationTable() { }
AttenuationConfigurationTable::~AttenuationConfigurationTable() { }
class Attenuation_configuration_table
{
struct attenuation_voltages_struct
{
float att_value;
float v1;
float v2;
} ;
struct frequency_tables_struct
{
int frequency;
attenuation_voltages_struct attenuation_voltages[100];
int voltages_count = 0;
} ;
frequency_tables_struct _frequency_tables[42];
public:
/************************************************************************/
/* load the table in this object from the given flash memory address */
/************************************************************************/
void load_attenuation_calibration_table_from_flash(flash_entry_struct memory_address[])
{
// bunch of logic here...
}
};
The h file for the class:
#ifndef ATTENUATIONCONFIGURATIONTABLE_H_
#define ATTENUATIONCONFIGURATIONTABLE_H_
#include "flashEntryStruct.h"
class AttenuationConfigurationTable
{
public:
AttenuationConfigurationTable();
virtual ~AttenuationConfigurationTable();
void load_attenuation_calibration_table_from_flash(flash_entry_struct flash_memory_address[]);
};
#endif /* ATTENUATIONCONFIGURATIONTABLE_H_ */
And, just for completeness, the h file defining the parameter structure:
#ifndef FLASHENTRYSTRUCT_H_
#define FLASHENTRYSTRUCT_H_
struct flash_entry_struct
{
uint16_t frequency;
uint16_t scaled_db;
int8_t v1_byte;
int8_t v2_byte;
} ;
#endif /* FLASHENTRYSTRUCT_H_ */
EDIT: the error message itself:
Invoking: Cygwin C++ Linker
g++ -o "HelloCPP.exe" ./src/AttenuationConfigurationTable.o ./src/Hello2.o ./src/HelloCPP.o
/usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: ./src/HelloCPP.o:/cygdrive/c/Users/ralph/files/programming/workspaces/HelloCPP/HelloCPP/Debug/../src/HelloCPP.cpp:15: undefined reference to `AttenuationConfigurationTable::load_attenuation_calibration_table_from_flash(flash_entry_struct*)'
collect2: error: ld returned 1 exit status
make: *** [makefile:58: HelloCPP.exe] Error 1
"make all" terminated with exit code 2. Build might be incomplete.

Answer 1

You declare AttenuationConfigurationTable in the header file with the load_attenuation_calibration_table_from_flash function, but then the function with the same name in the implementation file is inside the definition for another class, Attenuation_configuration_table.
Take the implementation for load_attenuation_calibration_table_from_flash out of the class definition for Attenuation_configuration_table in your cpp file, and define it instead as
void AttenuationConfigurationTable::load_attenuation_calibration_table_from_flash(/* ... */) {
// ...
}
This is the same syntax already used for the constructor and destructor in that file.
In the end, your header should look something like this:
class AttenuationConfigurationTable
{
public:
AttenuationConfigurationTable();
virtual ~AttenuationConfigurationTable();
void load_attenuation_calibration_table_from_flash(flash_entry_struct flash_memory_address[]);
private:
struct attenuation_voltages_struct
{
float att_value;
float v1;
float v2;
} ;
struct frequency_tables_struct
{
int frequency;
attenuation_voltages_struct attenuation_voltages[100];
int voltages_count;
} ;
frequency_tables_struct _frequency_tables[42];
};
and your cpp file should look something like this:
AttenuationConfigurationTable::AttenuationConfigurationTable() { }
AttenuationConfigurationTable::~AttenuationConfigurationTable() { }
void AttenuationConfigurationTable::load_attenuation_calibration_table_from_flash(/* params */) {
// body
}