Compound literals doesn't work

Using Arduino Programming Questions
1

When I use compound literals like

#define VECTOR_ROOT_E131_DATA (uint8_t[]){0x00, 0x00, 0x00, 0x04}

I get following error message:

lib/sACN/src/sACNDefs.h:76:42: error: taking address of temporary array
   76 | #define VECTOR_ROOT_E131_DATA (uint8_t[]){0x00, 0x00, 0x00, 0x04}

The compound literals works fine when using code runner on macOS with clang.

Here is an example for Arduino IDE using Raspberry Pi Pico

#define ACN_IDENTIFIER "ASC-E1.17\0\0\0"
uint8_t identifier[12] = "ASC-E1.17";
uint8_t ident[12] = {0};

//#define VECTOR_ROOT_E131_DATA 0x00000004
#define VECTOR_ROOT_E131_DATA (uint8_t[]){0x00, 0x00, 0x00, 0x04}
uint8_t vector[4] = {0x00, 0x00, 0x00, 0x04};
uint8_t vec[4] = {0};

void setup() {
	Serial.begin(9600);

	int equal1 = memcmp(identifier, ACN_IDENTIFIER, 12);
	printf("ACN compare %d\n", equal1);
	memcpy(ident, ACN_IDENTIFIER, 12);
	Serial.printf("ACN %s\n", ident);
	
	int equal2 = memcmp(vector, VECTOR_ROOT_E131_DATA, 4);
	printf("Vector compare %d\n", equal2);
	memcpy(vec, VECTOR_ROOT_E131_DATA, 4);
	Serial.printf("Vector 0x%x 0x%x 0x%x 0x%x\n", vec[0], vec[1], vec[2], vec[3]);

}

void loop() {
  // put your main code here, to run repeatedly:

}

and the error message:


FQBN: rp2040:rp2040:rpipico
Using board 'rpipico' from platform in folder: /Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5
Using core 'rp2040' from platform in folder: /Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5

Detecting libraries used...
/Users/sstaub/Library/Arduino15/packages/rp2040/tools/pqt-gcc/2.2.0-d04e724/bin/arm-none-eabi-g++ -I /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/core -c -Werror=return-type -Wno-psabi -DCFG_TUSB_MCU=OPT_MCU_RP2040 -DUSBD_PID=0x000a -DUSBD_VID=0x2e8a -DUSBD_MAX_POWER_MA=250 -DUSB_MANUFACTURER="Raspberry Pi" -DUSB_PRODUCT="Pico" -DPICO_CYW43_ARCH_THREADSAFE_BACKGROUND=1 -DCYW43_LWIP=1 -DLWIP_IPV6=0 -DLWIP_IPV4=1 -DLWIP_IGMP=1 -DLWIP_CHECKSUM_CTRL_PER_NETIF=1 -DARDUINO_VARIANT="rpipico" -DTARGET_RP2040 -DPICO_FLASH_SIZE_BYTES=2097152 -march=armv6-m -mcpu=cortex-m0plus -mthumb -ffunction-sections -fdata-sections -fno-exceptions -DARM_MATH_CM0_FAMILY -DARM_MATH_CM0_PLUS -iprefix/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/ @/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/lib/platform_inc.txt -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/include -fno-rtti -std=gnu++17 -g -pipe -w -x c++ -E -CC -DF_CPU=133000000L -DARDUINO=10607 -DARDUINO_RASPBERRY_PI_PICO -DBOARD_NAME="RASPBERRY_PI_PICO" -DARDUINO_ARCH_RP2040 -Os -DWIFICC=CYW43_COUNTRY_WORLDWIDE -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/cores/rp2040 -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/variants/rpipico /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/sketch/Compound_Literal.ino.cpp -o /dev/null
Generating function prototypes...
/Users/sstaub/Library/Arduino15/packages/rp2040/tools/pqt-gcc/2.2.0-d04e724/bin/arm-none-eabi-g++ -I /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/core -c -Werror=return-type -Wno-psabi -DCFG_TUSB_MCU=OPT_MCU_RP2040 -DUSBD_PID=0x000a -DUSBD_VID=0x2e8a -DUSBD_MAX_POWER_MA=250 -DUSB_MANUFACTURER="Raspberry Pi" -DUSB_PRODUCT="Pico" -DPICO_CYW43_ARCH_THREADSAFE_BACKGROUND=1 -DCYW43_LWIP=1 -DLWIP_IPV6=0 -DLWIP_IPV4=1 -DLWIP_IGMP=1 -DLWIP_CHECKSUM_CTRL_PER_NETIF=1 -DARDUINO_VARIANT="rpipico" -DTARGET_RP2040 -DPICO_FLASH_SIZE_BYTES=2097152 -march=armv6-m -mcpu=cortex-m0plus -mthumb -ffunction-sections -fdata-sections -fno-exceptions -DARM_MATH_CM0_FAMILY -DARM_MATH_CM0_PLUS -iprefix/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/ @/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/lib/platform_inc.txt -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/include -fno-rtti -std=gnu++17 -g -pipe -w -x c++ -E -CC -DF_CPU=133000000L -DARDUINO=10607 -DARDUINO_RASPBERRY_PI_PICO -DBOARD_NAME="RASPBERRY_PI_PICO" -DARDUINO_ARCH_RP2040 -Os -DWIFICC=CYW43_COUNTRY_WORLDWIDE -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/cores/rp2040 -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/variants/rpipico /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/sketch/Compound_Literal.ino.cpp -o /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/629566102/sketch_merged.cpp
/Users/sstaub/Library/Arduino15/packages/builtin/tools/ctags/5.8-arduino11/ctags -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/629566102/sketch_merged.cpp
Compiling sketch...
/Users/sstaub/Library/Arduino15/packages/rp2040/tools/pqt-python3/1.0.1-base-3a57aed/python3 -I /Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/tools/signing.py --mode header --publickey /Users/sstaub/Documents/Arduino/Compound_Literal/public.key --out /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/core/Updater_Signing.h
/Users/sstaub/Library/Arduino15/packages/rp2040/tools/pqt-gcc/2.2.0-d04e724/bin/arm-none-eabi-g++ -I /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/core -c -Wall -Wextra -Werror=return-type -Wno-ignored-qualifiers -Wno-psabi -DCFG_TUSB_MCU=OPT_MCU_RP2040 -DUSBD_PID=0x000a -DUSBD_VID=0x2e8a -DUSBD_MAX_POWER_MA=250 "-DUSB_MANUFACTURER=\"Raspberry Pi\"" "-DUSB_PRODUCT=\"Pico\"" -DPICO_CYW43_ARCH_THREADSAFE_BACKGROUND=1 -DCYW43_LWIP=1 -DLWIP_IPV6=0 -DLWIP_IPV4=1 -DLWIP_IGMP=1 -DLWIP_CHECKSUM_CTRL_PER_NETIF=1 "-DARDUINO_VARIANT=\"rpipico\"" -DTARGET_RP2040 -DPICO_FLASH_SIZE_BYTES=2097152 -march=armv6-m -mcpu=cortex-m0plus -mthumb -ffunction-sections -fdata-sections -fno-exceptions -DARM_MATH_CM0_FAMILY -DARM_MATH_CM0_PLUS -MMD -iprefix/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/ @/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/lib/platform_inc.txt -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/include -fno-rtti -std=gnu++17 -g -pipe -DF_CPU=133000000L -DARDUINO=10607 -DARDUINO_RASPBERRY_PI_PICO "-DBOARD_NAME=\"RASPBERRY_PI_PICO\"" -DARDUINO_ARCH_RP2040 -Os -DWIFICC=CYW43_COUNTRY_WORLDWIDE -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/cores/rp2040 -I/Users/sstaub/Library/Arduino15/packages/rp2040/hardware/rp2040/3.9.5/variants/rpipico /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/sketch/Compound_Literal.ino.cpp -o /private/var/folders/vd/yv1mb7lx6gn7ymffgtjk6hx80000gn/T/arduino/sketches/0CD56E42A202B01F908E5D10B761265C/sketch/Compound_Literal.ino.cpp.o
/Users/sstaub/Documents/Arduino/Compound_Literal/Compound_Literal.ino: In function 'void setup()':
/Users/sstaub/Documents/Arduino/Compound_Literal/Compound_Literal.ino:6:42: error: taking address of temporary array
    6 | #define VECTOR_ROOT_E131_DATA (uint8_t[]){0x00, 0x00, 0x00, 0x04}
      |                                          ^~~~~~~~~~~~~~~~~~~~~~~~
/Users/sstaub/Documents/Arduino/Compound_Literal/Compound_Literal.ino:18:37: note: in expansion of macro 'VECTOR_ROOT_E131_DATA'
   18 |         int equal2 = memcmp(vector, VECTOR_ROOT_E131_DATA, 4);
      |                                     ^~~~~~~~~~~~~~~~~~~~~
/Users/sstaub/Documents/Arduino/Compound_Literal/Compound_Literal.ino:6:42: error: taking address of temporary array
    6 | #define VECTOR_ROOT_E131_DATA (uint8_t[]){0x00, 0x00, 0x00, 0x04}
      |                                          ^~~~~~~~~~~~~~~~~~~~~~~~
/Users/sstaub/Documents/Arduino/Compound_Literal/Compound_Literal.ino:20:21: note: in expansion of macro 'VECTOR_ROOT_E131_DATA'
   20 |         memcpy(vec, VECTOR_ROOT_E131_DATA, 4);
      |                     ^~~~~~~~~~~~~~~~~~~~~

exit status 1

Compilation error: taking address of temporary array
2

Well, it appears to compile OK (ESP32-C3) if you wrap the "compound literal" in quotes. Does it do what you want, though ?
#define VECTOR_ROOT_E131_DATA "(uint8_t[]){0x00, 0x00, 0x00, 0x04}"

3

There's a discussion about it here: taking address of temporary array

Why are you so averse to declaring space for this little array?

4

Thank you for that hint. But I don't know why it is necessary, is it a GCC problem?
EDIT: This doesn't work. Yes you can compile but the content of the array is now completely wrong.

5

Not really a surprise - you are passing a string literal - the compiler is not trying to parse it as an array declaration.

6

In C, compound literals are allowed, and you can create temporary arrays but you cannot take the address of a temporary array because they are not stored in a persistent location.

In C++, compound literals are not part of the language.

7

But you can do it with clang compiler.

8

OK. I see why it compiled when in quotes. I regretably looked no further.
This appears to work:
#define VECTOR_ROOT_E131_DATA (const uint8_t *)((const uint8_t[]){0x00, 0x00, 0x00, 0x04})
However, I'm sure that @J-M-L's comment should not be ignored.

EDIT

or even this:
#define VECTOR_ROOT_E131_DATA (const uint8_t[]){0x00, 0x00, 0x00, 0x04}

9

The last example works as expected.

10

The const might make it a permanent array and then you can get its address

11

"static const" ?

12

Somewhere in flash where it can be addressed on the right architecture