How to snprintf uint64_t?

[douglas.malnati]

Using WSL2, NCS 2, VSCode.

I tried to snprintf("%ull\n", (uint64_t)5) but I only see "ul" printed to the screen.

Here are the relevant prj.conf values

CONFIG_CPLUSPLUS=y

CONFIG_LIB_CPLUSPLUS=y

CONFIG_NEWLIB_LIBC=y

CONFIG_STD_CPP20=y

CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y

CONFIG_CBPRINTF_FP_SUPPORT=y

Can you tell me the right way to print uint64_t values in decimal?

Thanks.

[Sigurd Hellesvik]

Hi,

I found this stackoverflow article saying that the "lu" print can be from newlib nano:

Try to set CONFIG_NEWLIB_LIBC_NANO=n.
Remember to check if this configuration will have other side-effects on your project.

Regards,
Sigurd Hellesvik

[douglas.malnati]

That didn't fix it, and that parameter doesn't appear to be in effect anyway with the parameters I chose above.

What else can I do?

Thanks.

[Sigurd Hellesvik]

Here is a sample where I print an uint64_t.

Does it help?

print_uint64_sample.zip

Regards,
Sigurd Hellesvik

[douglas.malnati]

I see you're using the same prj.conf parameters as me, and then you do a printf with the "%llu" parameter (I had mistakenly wrote "%ull" before).

I can't tell if your printf works or not because my system isn't set up to redirect printf to UART.  I'd actually like to be able to do that, though, do you know what I need to do to set that?  I'm very unclear on how the various backends work.

I'm dimly aware that implementing a _write() function, under some circumstances, intercepts the bytes sent to stdout.

I have a full personal logging system that sends all of its data to UART0.  I could easily send whatever was meant for stdout to that.

How can I do that?  Then I'll be able to test the printf.

All the prj.conf values that affect output I have below here.  Please let me know!

# I want serial enabled in general
CONFIG_SERIAL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_UART_1_INTERRUPT_DRIVEN=y
CONFIG_UART_ASYNC_API=y
CONFIG_UART_LINE_CTRL=y

# I want logging to function
CONFIG_LOG=y

# I want to use the serial interface for logging
# but when I enable shell, this makes printf'd material come out twice,
# once normally, and another time with the shell prefix.
# so I'm disabling it for now.
# CONFIG_LOG_BACKEND_UART=y

# I want synchronous logging (no queue and print later)
CONFIG_LOG_MODE_IMMEDIATE=y

# I want to be able to influnce what gets logged at runtime (via shell)
CONFIG_LOG_RUNTIME_FILTERING=y

# I want the default to be that every module prints all levels
# 0 = off
# 1 = error
# 2 = error and warning
# 3 = error and warning and info
# 4 = error and warning and info and debug
CONFIG_LOG_DEFAULT_LEVEL=4

# show function name in output
CONFIG_LOG_FUNC_NAME_PREFIX_ERR=y
CONFIG_LOG_FUNC_NAME_PREFIX_WRN=y
CONFIG_LOG_FUNC_NAME_PREFIX_INF=y
CONFIG_LOG_FUNC_NAME_PREFIX_DBG=y

# color it
CONFIG_LOG_BACKEND_SWO=y
CONFIG_LOG_BACKEND_SHOW_COLOR=y

# redirect printk to the log
# I am disabling this, because when shell enabled, prink output was
# prefixed with shell.  now I see it on serial with no prefix.
#CONFIG_LOG_PRINTK=y




# ##### Shell #####

# # I want the shell interface to operate
CONFIG_SHELL=y

Thanks!

[douglas.malnati]

Nevermind about printf, I found out how to do it:

• (link) StackOverflow link showing to override the _write() call
• (link) Zephyr libc-hooks.c weak _write() call

(there's a re-entrant version _write_r() I also implemented)

Anyway so I can intercept printf output now, and I still see it's not working.

Do you see snprintf working for you?  That is actually what I want to get working.

What is the best way to track down what's not working here?

Thanks!

[Sigurd Hellesvik]

Hi,

Due to low staffing this week, answers may take longer than normal.

Regards,
Sigurd Hellesvik

[douglas.malnati]

Ok thanks, please help when you can.

[Sigurd Hellesvik]

From snprintf documentation, this function prints to a string and not as an output.

Moreover, when you describe it as snprintf("%ull\n", (uint64_t)5), you have 1 argument, but the snprintf needs 3 inputs.

What do you want to use sprintf for?

Regards,
Sigurd Hellesvik

[douglas.malnati]

Hi, I was using the snippet of code as shorthand for what I was doing in principle.

Here is how the code works.  I'm wrapping the snprintf in a convenience function to make it easier to call.  I'm converting values to strings.

static const uint8_t BUF_SIZE = 64;
static char BUF[BUF_SIZE];

template <typename T>
const char *StrC(const char *fmt, T val)
{
    int bufSize = snprintf(BUF, BUF_SIZE, fmt, val);

    return FormatTemplateBase::BUF;
}

The point is that when I use the format string for uint64_t it doesn't work as described above, even when used outside of the wrapper.

Can you help?

Thanks.

[Sigurd Hellesvik]

Is this what you are looking for?

snprintf_uint64_t_test.zip

main.c:

#include <zephyr/kernel.h>
#include <stdio.h>

void main(void)
{
    uint8_t test[20] = "test";
    uint64_t num = 111111111111111;
    snprintf(test, 20, "%llu", num);
	printk("Hello World! %s\n", test);
}

Board: nrf52840dk_nrf52840

nRF Connect SDK: v2.3.0

Regards,
Sigurd Hellesvik