David Herregat

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

12 years, 5 months ago.

char error on compiling

Hi all,

I have no c++ experience, so i'm stuck with a simple test program that gets the following error:

"a value of type "const char [4]" cannot be used to initialize an entity of type "char [3]"" in file "/main.cpp", Line: 5, Col: 16

The Code:

  1. include "mbed.h"

Serial pc(USBTX, USBRX); tx, rx

char slaveid[3]="ABC";

int main() { pc.printf("Slave id %s",slaveid);

while(1) { char c = pc.getc(); if(c == 'u'){ pc.printf("C pressed"); } if(c == 'd'){ pc.printf("D pressed"); }

} }

1 Answer

Jonas Lannoo
12 years, 5 months ago.

Hi,

Maybe you could use this:

line 4 new

char* slaveid = "ABC";

instead of your code:

line 4 old

char slaveid[3]="ABC";

That should work. :)

Jonas

Accepted Answer

Thanks Jonas ...

Is there some mbed c++ programming tutorials/documentation available ?

posted by David Herregat 18 May 2013

For documentation I generally use: http://www.cplusplus.com/

What is most often used is:

char slaveid[] = "ABC";

The problem is a bit shown here: http://www.cplusplus.com/doc/tutorial/ntcs/. Slaveid is basicly a pointer that points to where the first letter of your string is stored. The next letter is stored in the byte after that, etc. However if you pass slaveid to a function, when that function reads your string it needs to know when it has reached the last symbol of your string. That's why at the end of every string like this a NULL terminator is placed, which tells any function reading slaveid that it reached the end of slaveid.

And that is why your "ABC" has a length of 4 (3+null terminator), and you tried to fit it in slaveid which is only length 3.

posted by Erik - 18 May 2013

Thanks Erik, it makes sense now :)

posted by David Herregat 18 May 2013