The function printf does not print anything on the console

Hi all,

Recently, the function printf does not print any data to the console anymore. I did not face this issue before. I’ve read the threads with similar problems on this forum. However, not any solution worked for me. For example, I’ve added a ‘\n’ character at the end of the string, but this didn’t solve the problem.

Any ideas what can fix this problem? Thanks in advance!


Please share some code…

The code is shown below. When I run this code, an “empty” character is being printed in the console.

#include "mbed.h"

int main()
    printf("Hello World\n");

    while(1) {


    return 0;


Maybe it is related to a specific hardware or version of the Mbed OS or tools.
So what a version of MbedOS, a board and tools you use?

For me that printf working well on the MbedOS 6.2.1, Nucleo-F429ZI and Online Compiler.

BR, Jan

We’re using the Mbed OS 6 version, in combination with Mbed Studio. The microcontroller that we’re using is NUCLEO-F411RE.

I had the same problem with another board and added this code below #include “mbed.h” and it then worked:

    // Create a BufferedSerial object to be used by the system 
    // Check that the USBTX and USBRX are correctly defined in target pinnames files or define yourself
   //  Insert the baud rate you want to use
    static BufferedSerial serial_port(USBTX, USBRX, 115200);

    FileHandle *mbed::mbed_override_console(int fd)
        return &serial_port;
1 Like

thats strange, a printf() should always work. If the baudrate does not match, you can also set it in the mbed_app.json:

    "target_overrides": {
        "*": {
            "platform.stdio-baud-rate": 115200,
            "platform.stdio-convert-newlines": true

The STDIO_UART_TX/RX can be also remapped in the mbed_app.json, but the defaults work for the USB VCOM. Unless you have modified the solder jumpers on the Nucleo, the VCOM can be disconnected.

    // STDIO for console print

also PA_2 and PA_3 must not be connected to other hardware.

Yeah, I had the same problem. The ST default is 9600,8,N,1 and the mbed studio defaults are 115200,8,N,1 - just change the baud rate drop down for your board’s serial terminal to 9600 and it works fine.