Stringstream bug with mbed-os-6

Mbed OS Bugs
1

Hello,

I’m familiar with using stringstreams to format my serial or tcp communications.

But since mbed-os-6 I have a problem with inserting numbers parameters to the stream.

Example with mbed-os-5.15.3 work fine

#include "mbed.h"
#include <sstream>

Serial pc(USBTX, USBRX, 115200);

int main(void)
{
stringstream sstream;
sstream << "\nMbed OS " << MBED_VERSION;
pc.printf("%s", sstream.str().c_str());
}

Answer: Mbed OS 51503

Example with mbed-os-6.0.0 don’t work

#include "mbed.h"
#include <sstream>

UnbufferedSerial pc(USBTX, USBRX, 115200);

int main(void)
{
stringstream sstream;
sstream << "\nMbed OS " << MBED_VERSION;
pc.write(sstream.str().c_str(), sstream.str().size());
}

Answer: Mbed OS

I tried it with online compiler and mbed studio is the same thing.

Does anyone have any ideas on how to solve this problem?

Thank you,
YSI

2

Hi YSI,
please check this post from Kentaro Okuda .
So try to add into the mbed_app.json

{
	"target_overrides": {
	    "*": {
	        "target.printf_lib": "std"
	    }
	}
}

BR, Jan

3

Thank you Jan it works.

The releases note indicates minimal-printf is set by default with mbed-os-6.0 but does not indicate that it can be a breaking change.

Next time I’ll take “If your application requires more advanced functionality you’ll have to revert to using standard library version.” for a breaking change.

Thanks again Jan!