ESP-32 compiler bug

[thedispatcher]

A new error appeared when compiling code using the MF_MIDIfile library. I condensed the code to a simple program which exhibits the problem.

typedef struct
{
  uint8_t track;    ///< the track this was on
  uint16_t size;    ///< the number of data bytes
  uint8_t type;     ///< meta event type
  union
  {
    uint8_t data[50]; ///< byte data. Only 'size' bytes are valid
    char chars[50];   ///< string data. Only 'size' bytes are valid
  };
} meta_event;
#define ARRAY_SIZE(a) (sizeof(a)/sizeof((a)[0]))

void setup(void)
{
 uint32_t mLen;
 meta_event mev;
 mLen = 12;
  uint8_t minLen = min(ARRAY_SIZE(mev.data), mLen);
}
void loop(void){
}

If you compile this code for the Arduino Nano ESP32 it gives no error.
If you select the "ESP32 Dev Module", the "ESP32-WROOM-DA module", or the "DOIT ESP32 DEVKIT V1" (and probably others), it compiles with the following error (plus much more):

D:\Util\ArduinoSB\Sketchbook\MF_error\MF_error.ino:23:23: error: no matching function for call to 'min(unsigned int, uint32_t&)'

I am using IDE 2.3.4.

The Dispatcher

[ptillisch]

Hi @thedispatcher. When compiling for ESP32, both arguments to min must have the same data type:

max() not accepting #defined values

So you can fix the error by changing this line:

uint32_t mLen;

To this:

unsigned int mLen;

[gfvalvo]

@ptillisch

So you can fix the error by changing this line:

uint32_t mLen;

To this:

unsigned int mLen;

Interesting. The severity of the issue appears to vary with version of ESP32 Arduino Core. Anyway, since sizeof() produces type size_t, best would be:

	size_t mLen;

[gfvalvo]

You can also provide the template parameter to std::min. This will allow for implicit conversion of the argument types because the template no longer needs to be deduced.

  uint32_t mLen;
  meta_event mev;
  mLen = 12;
  uint8_t minLen = min<size_t>(ARRAY_SIZE(mev.data), mLen);

[thedispatcher]

Where would std:min be placed?

The suggestions are welcome. I have only 2 slight misgivings:

1. I don't like having to change the code of a published library.
2. "min()" is documented to accept parameters of any type. Should this be changed?

Thanks for the very prompt attention.
The Dispatcher

[gfvalvo]

@thedispatcher

Where would std:min be placed?

On ESP32, min() invokes std::min() from the Standard C++ Library (at least it does with ESP32 Arduino Core 3.07 where I tested it). So, the code in Post #4 works as-is.

@thedispatcher

"min()" is documented to accept parameters of any type. Should this be changed?

Any is an overly-strong statement. First, as @ptillisch noted, both parameters must be of the same type. Second, there must actually be a function available that determines which is greater ... min(Serial, Serial1); would be nonsense. You could say without argument that it works for all numeric types ... as long as both are the same type.