template <class T>: error: 'T' does not name a type

Question

I'm trying to compile some code that compile fine in Arduino IDE, in Visual Studio with support for Arduino (Visual Micro). This is the code with problems:

template <class T> int EEPROM_writeAnything(int ee, const T& value)
{
    const byte* p = (const byte*)(const void*)&value;
    unsigned int i;
    for (i = 0; i < sizeof(value); i++)
          EEPROM.write(ee++, *p++);
    return i;
}

template <class T> int EEPROM_readAnything(int ee, T& value)
{
    byte* p = (byte*)(void*)&value;
    unsigned int i;
    for (i = 0; i < sizeof(value); i++)
          *p++ = EEPROM.read(ee++);
    return i;
}

The error I'm getting is:

app.ino:43:40: error: 'T' does not name a type
:int EEPROM_writeAnything(int ee, const T& value)
app.ino:43:43: error: ISO C++ forbids declaration of 'value' with no type [-fpermissive]

Can someone please point me in the right direction?

Thanks.

Answer 1

I think i got the answer. You need to add declaration for the functions in Visual Studio manually.

template <class T> int EEPROM_writeAnything(int ee, const T& value);
template <class T> int EEPROM_readAnything(int ee, T& value);

but whereas Arduino IDE preprocess your source code and adds these automatically for you behind the scene. So it works in Arduino IDE.

Hint : When you enable verbose output in your arduino IDE, refer to the temporary path in which the intermediate files generated during compilation is saved. It should be something like %temp%\build0094e6ca87558f1142f08e49b0685193.tmp\sketch . It should have the following statements .

#line 2 "C:\\Users\\Sound\\Documents\\Arduino\\sketch_mar10d\\sketch_mar10d.ino"
template <class T> int EEPROM_writeAnything(int ee, const T& value);
#line 11 "C:\\Users\\Sound\\Documents\\Arduino\\sketch_mar10d\\sketch_mar10d.ino"
template <class T> int EEPROM_readAnything(int ee, T& value);
#line 21 "C:\\Users\\Sound\\Documents\\Arduino\\sketch_mar10d\\sketch_mar10d.ino"

To know more about this, read here.

Answer 2

This snippet compiles fine under GCC/Linux and MSVS 2015/Windows.

Q: Does it work for you? Is it OK with the Arduino IDE?

Q: Does it fail with "error: 'T' does not name a type" with Arduino (Visual Micro)? Have you contacted Visual Micro?

#include <stdio.h>

typedef unsigned char byte;

class A {
public:
  void write(int & ee, const byte &p) { }
};

A EEPROM;

template <class T> int EEPROM_writeAnything(int ee, const T& value)
{
    const byte* p = (const byte*)(const void*)&value;
    unsigned int i;
    for (i = 0; i < sizeof(value); i++)
          EEPROM.write(ee++, *p++);
    return i;
}

int main (int argc, char *argv[]) {
  printf ("Hello world\n");
}