No Printf output on UART before \n

[Gui_STM]

Good morning, I am trying to print a string on STM32F401RBT6 using vs code and Cmake, but I keep getting an issue, when I use '\n' the UART doesn't print nothing beyond the '\n', can somebody help me with this issue, please?

printf("Hello\n World");

[Andrew Neil · Accepted solution]

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@Gui_STM wrote:

 when I use '\n' the UART doesn't print nothing beyond the '\n',

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I presume you mean, "doesn't print anything beyond the \n" ?

This is defined behaviour: the printf output is line-buffered; so the output is not sent until a line is complete - ie, until it reaches a \n

https://community.st.com/t5/stm32-mcus/how-to-redirect-the-printf-function-to-a-uart-for-debug-messages/ta-p/49865#:~:text=Line%2Dbuffering%3A,sent%3B%20e.g.%2C

PS:

stderr is not buffered:

https://community.st.com/t5/stm32cubeide-mcus/retarget-printf-on-stm32g070rbxx-cortex-m0/m-p/721027/highlight/true#M30725

PPS:

Disable the buffering with:

setvbuf(stdout, NULL, _IONBF, 0);

https://community.st.com/t5/stm32-mcus-products/stm32h747-getchar-prototype-strangeness/m-p/618009/highlight/true#M229551

[Andrew Neil]

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@Andrew Neil wrote:
printf output is line-buffered

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To be more precise, the GCC default for stdout is line-buffered - so fprintf  (or anything else) to stdout would, by default, show the same effect.

[Tesla DeLorean]

Or sprintf() into HAL_UART_Transmit(), it returns a length

[Gui_STM]

Thank you, I will try this solution on my code.

[Gui_STM]

But how does this solve my problem with printing on my UART?

[Andrew Neil]

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@Gui_STM wrote:

But how does this solve my problem with printing on my UART?

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because your "problem" is due to the buffering performed by printf (strictly, by stdout).

By not using printf, you avoid that problem!