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Functions and error message

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Guest
Guest

Functions and error message

Posted: Mon Mar 07, 2005 11:09 am

Code:

#use delay(clock=4000000)
#fuses NOWDT,HS,PUT,NOPROTECT,BROWNOUT,NOCPD,NOWRT,NOLVP

int state;
int start;
int number;

void start_function()
{
if ( state == start)
{
new_function();
return;

}

}

void new_function()
{
output_high(PIN_B3);
number++;
}

main()
{

state = start;
while(1)
{
start_function();
}
}

Why do i get compiler error message:
Undefined identifier new function

Compiler version is 3.150

Guest

Posted: Mon Mar 07, 2005 11:28 am

Because you are using the function before it is declared. Just swap the order of the declarations:

Code:

#use delay(clock=4000000)
#fuses NOWDT,HS,PUT,NOPROTECT,BROWNOUT,NOCPD,NOWRT,NOLVP

int state;
int start;
int number;

void new_function()
{
output_high(PIN_B3);
number++;
}

void start_function()
{
if ( state == start)
{
new_function();
return;
}

}

main()
{
state = start;
while(1)
{
start_function();
}
}

ckielstra

Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

Posted: Mon Mar 07, 2005 11:31 am

Quote:

Why do i get compiler error message:
Undefined identifier new function

In your start_function() you are calling new_function() before it is declared. A C-compiler must know about the parameters used and returned by a function before it can be used in another function.
Think about the C-compiler as starting to read at the beginning of your program and translating it to assembly language 'on the fly'. When the compiler comes across a function name it doesn't know it shows the given error message. Some other computer languages are 'smarter' in this respect where the compiler first scans the whole program to learn all function names in the program.

The solution is to tell the compiler all function names at the start of your program, this is called 'declaration' and consists of the function name and all parameters and the return type. A function 'definition' is the implementation of the function.

Code:

#use delay(clock=4000000)
#fuses NOWDT,HS,PUT,NOPROTECT,BROWNOUT,NOCPD,NOWRT,NOLVP

int state;
int start;
int number;

////////////////////////////////////////////////////////
// Function declarations
////////////////////////////////////////////////////////
void start_function();
void new_function();
void main();

////////////////////////////////////////////////////////
// Implementation
////////////////////////////////////////////////////////

void start_function()
{
if ( state == start)
{
new_function();
return;

}

}

void new_function()
{
output_high(PIN_B3);
number++;
}

main()
{

state = start;
while(1)
{
start_function();
}
}

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