ESP32 Forum

Posted: **Fri Oct 27, 2017 10:41 pm**

Hello. This is my first post.

I am able to successfully build and run the hello_world application on a SparkFun ESP32 Thing module (26MHz main xtal).

However, I observer that whereas these lines in the example:

Code: Select all

    for (int i = 10; i >= 0; i--) {
        printf("Restarting in %d seconds...\n", i);
        vTaskDelay(1000 / portTICK_PERIOD_MS);
        }

work correctly, these altered lines do not output the "." character:

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    int i=10;
    printf("Restarting in %d seconds \n", i);
    for (; i >= 0; i--) {
        printf(".");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }

but these do (but are not in the format that I want):

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    int i=10;
    printf("Restarting in %d seconds \n", i);
    for (; i >= 0; i--) {
        printf(".\n");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }

IOW, it appears that a call to printf() does not result in output to the terminal until a \n is injected into printf()'s arguments.

Based on my previous experience with printf() on embedded systems, this is not normal behavior. Is this intentional? Is there some option I need to set to ensure that whatever I send via printf() is output to the terminal, without requiring a \n?

Thanks,

Posted: **Sun Oct 29, 2017 6:34 am**

By default, output streams have line buffering enabled.

You can configure buffering for any particular stream using setvbuf function.

More info:
http://en.cppreference.com/w/c/io/setvbuf
https://github.com/espressif/newlib-esp ... vbuf.c#L20

For example,

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setvbuf(stdout, NULL, _IONBF, 0);

disables buffering on stdout.

Note that you will generally get better performance if buffering is used. You can also use fflush(stdout) to flush the buffer without sending a newline.

Posted: **Fri Nov 03, 2017 9:18 pm**

Thank you -- I suspected something like that, but didn't know where to look.

Thanks again,

ESP32 Forum

printf() requires a \n for output?

printf() requires a \n for output?

Re: printf() requires a \n for output?

Re: printf() requires a \n for output?