Error at compiling

Questions » Error at compiling

6 years, 7 months ago.

I want to print this variable :

main

 printf(ubidotsGET(TOKEN, VARIABLE_ID)); //Line:18

and I´m getting this errors:

Error: Argument of type "const char *" is incompatible with parameter of type "std::uint8_t *" in "main.cpp", Line: 18, Col: 24

Error: Argument of type "const char *" is incompatible with parameter of type "std::uint8_t *" in "main.cpp", Line: 18, Col: 31

Error: Argument of type "std::uint8_t *" is incompatible with parameter of type "const char *" in "main.cpp", Line: 18, Col: 13

That variable comes from a .h and .c files:

library.c

uint8_t* ubidotsGET( uint8_t* token,  uint8_t* variable_id ){
    memset(&buffer, 0,sizeof(buffer));
    sprintf(buffer,"http://www.things.com/variables/%*s/?token=%*s",sizeof(variable_id),variable_id,sizeof(token),token);
    return buffer;}

and

library.h

#define TOKEN           "123a"
#define VARIABLE_ID     "abc2"
 uint8_t* ubidotsGET( uint8_t* token,  uint8_t* variable_id );

Any idea what im doing wrong, I imported this from a c library on mplab?

1 Answer

6 years, 7 months ago.

Hello Daniel,

printf function is declared as:

int printf ( const char * format, ... );

So you have to pass it a const char* type.

Find buffer and make sure it's a const char* type for example as follows:

char buffer[256]; // the size could be different

NOTE: Array type variables are always const pointers.

Then change:

library.h

#define TOKEN           "123a"
#define VARIABLE_ID     "abc2"
const char* ubidotsGET(const char* token, const char* variable_id );

and

library.c

const char* ubidotsGET(const char* token, const char* variable_id ){
    memset(&buffer, 0,sizeof(buffer));
    sprintf(buffer,"http://www.things.com/variables/%*s/?token=%*s",sizeof(variable_id),variable_id,sizeof(token),token);
    return buffer;
}

Another option is to modify only

library.c

uint8_t* ubidotsGET(const char* token, const char* variable_id ){
    memset(&buffer, 0,sizeof(buffer));
    sprintf(buffer,"http://www.things.com/variables/%*s/?token=%*s",sizeof(variable_id),variable_id,sizeof(token),token);
    return (uint8_t*)buffer;
}

and format the variable passed to print as string:

main.cpp

pc.printf("%s", ubidotsGET(TOKEN, VARIABLE_ID));

NOTE: %d would not work correctly since it formats the variable as signed decimal integer.

Accepted Answer

I tried and i got some other error, this is the whole code https://developer.mbed.org/users/dan_cuspi/code/C-Conv/

posted by J Daniel Martinez C 01 Sep 2017

Sorry I did not notice it before, but since the ubidotsGET function is implemented in a standard 'C' file (library.c) but called from a 'C++' file (main.cpp) so the compiler applies function name mangling and that's why the linker is not able to find it. There are two solutions:

Either Modify the declaration of ubidotsGET function in the 'library.h' file as follows:

library.h

#ifdef __cplusplus 
extern "C" {
#endif
uint8_t* ubidotsGET(const char* token, const char* variable_id);
#ifdef __cplusplus
}
#endif

Or rename the 'library.c' file to 'library.cpp', and (in order to match the function definition) modify the function declaration as below:

library.h

uint8_t* ubidotsGET(const char* token, const char* variable_id);

NOTE: The compiler will still report a warning "argument of type "uint8_t*" is incompatible with parameter of type "char*" but finish with success and the program will work. However, the warning could be removed if you use the first option proposed in my first answer (but you should rename the 'library.c' file to 'library.cpp'). Then in the 'main.cpp' you can call either:

main.cpp

pc.printf(ubidotsGET(TOKEN, VARIABLE_ID));

main.cpp

pc.printf("%s", ubidotsGET(TOKEN, VARIABLE_ID));

with the same result.

posted by Zoltan Hudak 01 Sep 2017

Thank you, is working now !!

posted by J Daniel Martinez C 08 Sep 2017

J Daniel Martinez C

Important changes to forums and questions

6 years, 7 months ago.