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passing char and returning 1-wire DeviceAddress

PeteDD (62)
I am working on a config.ini parser combined with a class that manages sensors in a large data collection system. One type of sensors we are using are 1-Wire which have address of the type deviceAddress which is an array of eight uint8_t. I am using the excellent code inifile by Steve Marple to which I have added code for handling 1-Wire addresses in the form "0x12:0x34:0x56:0x78:0x90:0x12:0x34:0x56" which works well but I do not want to repeat that block of code over and over again so I am trying to figure out how to move it out into a separate function.

Here is a simplification of the inifile code I am using:

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    const size_t bufferLen = 80;
    char buffer[bufferLen];
    const char *filename = "/config.ini";
// SDI, SD, and INIFILE startup code goes here and we open and read the ini file

// now we grab the 1-wire address from the ini file
    ini.getValue("S_1WIRE_1", "ADDR", buffer, bufferLen); 

// and unpack the content with a bit of error checking 
//*******   
    uint8_t addr[8];
    int len = -1;
    if (sscanf(buffer, "%x:%x:%x:%x:%x:%x:%x:%x%n", addr + 0, addr + 1, addr + 2, addr + 3, addr + 4, addr + 5, addr + 6, addr + 7, &len) < 8 || len < 15)
    {
      Serial.println("ERROR IN CONFIG.INI   malformed 1-Wire address");
      Serial.println("HALTING");
      for (;;);
//*****
// and then put the address bytes into the class object member data for the address
               
      for (uint8_t i = 0; i < 8; i++)
      {
          S_1WIRE_1.SetAddressByte(addr[i], i);
      }


I also have a class method for taking the whole address of the 1-Wire type deviceAddress 
 
 
S_1WIRE_1.SetAddress(deviceAddress address)


What I would really like to do is to take this code between the //**** lines above and put it in a separate function to return the deviceAddress such that I could call it in a form like this (but correct)

 
 
S_1WIRE_1.SetAddress(AddressUnpackingFunction(buffer));


I have tried a number of approaches to build a
deviceAddress* AddressUnpackingFunction(char* buffer)

function which would include code like this to build a deviceAddress type variable to return: 
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    deviceAddress tmpAddr;
    for(uint8_t i=0;i<8;i++)
    {
      tmpAddr[i] = addr[i];
    }


or more simply something like...
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deviceAddress* AddressUnpackingFunction(char* buffer)
{
    DeviceAddress addr[8];
    int len = -1;
    if (sscanf(buffer, "%x:%x:%x:%x:%x:%x:%x:%x%n", addr + 0, addr + 1, addr + 2, addr + 3, addr + 4, addr + 5, addr + 6, addr + 7, &len) < 8 || len < 15)
    {
      Serial.println("ERROR IN CONFIG.INI   malformed 1-Wire address");
      Serial.println("HALTING");
      for (;;);
    }
    return (&addr);
}


but have failed to make it work.

I am certain there is a simple combination of pointers, dereferencing, and perhaps converting the char to a std::string that would work but it alludes me.

Could someone give me a quick kick in the butt to get this straight? THANKS!
Last edited on
Ganado (6810)
In your last code excerpt, DeviceAddress addr[8]; is a local variable. The memory for it will no longer exist once AddressUnpackingFunction returns (local variables "pop" off the stack; in C++ standardese these are objects with "automatic" storage duration). You need the memory to persist after the call is done.

If you still wanted the function to return a pointer to an array, that's fine, but the array needs to be in a larger scope (e.g. in the calling function's scope). One way to do this is to pass the addr array into the function.

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DeviceAddress* AddressUnpackingFunction(char* buffer, DeviceAddress addr[])
{
    int len = -1;
    if (sscanf(buffer, "%x:%x:%x:%x:%x:%x:%x:%x%n", addr + 0, addr + 1, addr + 2, addr + 3, addr + 4, addr + 5, addr + 6, addr + 7, &len) < 8 || len < 15)
    {
      Serial.println("ERROR IN CONFIG.INI   malformed 1-Wire address");
      Serial.println("HALTING");
      for (;;);
    }
    return addr;
}


This makes the calling code one line longer:
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DeviceAddress addr[8];
S_1WIRE_1.SetAddress(AddressUnpackingFunction(buffer, addr));


But, if S_1WIRE_1.SetAddress copies the addr array's memory into its own memory that it owns, then you could call SetAddress within your function -- then, you could just have DeviceAddress addr[8] be a variable local to the function, because it will no longer be used once the function is over. But I don't have documentation for the SetAddress function.
Last edited on
PeteDD (62)
Thank you Ganado for the good insights that will help me.
The address does end up in member data of the S_1WIRE_1 object. Since there are multiple of these objects and each has a section in the config.ini file, I end up making the S_1WIRE_*,SetAddress call for each of them from the config.ini parsing program. ("*" here is a wildcard digit).
Thanks again,
Pete
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