c++ array initialization on nRF9160

RE: c++ array initialization on nRF9160

Didrik Rokhaug — Thu, 06 Jan 2022 10:41:57 GMT

Hi, and sorry for the late reply.

Like I said, I am not familiar enough with the intricacies of C++ to tell you why your attempt didn't work. I could try to read up on it, though you might get a faster and better reply in the cpp channel on Zephyr's Discord server.

You can find a link to join the Discord server here: https://docs.zephyrproject.org/latest/getting_started/index.html#asking-for-help

Best regards,

Didrik

RE: c++ array initialization on nRF9160

WhiteCloud2 — Mon, 27 Dec 2021 15:45:59 GMT

Hi, Didrik,

Thanks for looking into it and the tip.

Yes, changing the definition of Inherit indeed leads to correct initialization. It also works for C++17, which I have been using. In addition, if I change the array declaration and do not specify the number of elements, i.e. from [1] to [], then it also works. So the next question is what is wrong, if any, in the original declaration? The issue appears to be a compiler bug since the same program runs correctly compiled using GCC on either a Linux PC or on other IoT devices.

Thanks

RE: c++ array initialization on nRF9160

Didrik Rokhaug — Mon, 27 Dec 2021 13:38:21 GMT

Hi,

I am not familiar enough with C++, and it's different versions, but if I change the definition of inherit to

static Inherit inherit[1] = {
        Inherit{{.words = 0xffffffff}}
};

and build test_init with C++2a (the default is 11), I get

[overlay] 4

FF FF FF FF 

[inherit] 4

FF FF FF FF

You can change the C++ version to 2a by adding the following config options to your prj.conf file.

CONFIG_CPLUSPLUS=y
CONFIG_STD_CPP2A=y

Best regards,

Didrik

RE: c++ array initialization on nRF9160

WhiteCloud2 — Fri, 24 Dec 2021 17:17:48 GMT

I have narrowed it down further to the following example and attached the updated project.

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct Data {
    uint32_t words;
};

struct Overlay {
    Data val;
};

struct Inherit : Data {
};

static Overlay overlay[1] = {
        {{.words = 0xffffffff}}
};

static Inherit inherit[1] = {
        {{.words = 0xffffffff}}
};

void print_struct(const char *title, const uint8_t *cbuf, int len)
{
    printf("[%s] %d\n", title, len);
    for (int i = 0; i < len; i++) {
        printf("%02X ", cbuf[i]);
    }
    printf("\n");
}

int main() 
{
    print_struct("overlay", (const uint8_t *) &overlay[0], sizeof(overlay[0]));   // FF FF FF FF
    print_struct("inherit", (const uint8_t *) &inherit[0], sizeof(inherit[0]));   // 00 00 00 00  <--- Incorrect?

    return 0;
}

devzone.nordicsemi.com/.../test_5F00_init.zip