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.

[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