Peculiarities of POWER C

When writing software in POWER C, there are some peculiarities that must be accounted for. POWER C is a programming language from 1986, meaning that its keywords and its syntax are pre C89 / ANSI C, which had been defined as a standard in 1989. In this article I am documenting the things I noticed when writing software in POWER C. This is by far no complete list.

Commenting a single line

Not working	Working
// This is a comment	/* This is a comment */

Initializing an array right after declaring it

Not working	Working
int arr[] = { 1,2,3 };	int arr[]; arr[0] = 1; arr[1] = 2; arr[3] = 3;

Counting the elements in a fixed-size array

Not working	Working
int arr[5] = {10, 20, 30, 40}; size_t n = sizeof(arr) / sizeof(arr[0]); printf(„The array has %zu elements.\n“, n);	int arr[5]; arr[0] = 10; arr[1]=20; arr[2]=30; arr[3]=40; arr[4] = ‚\0‘; int n = 0; while(arr[n] != ‚\0‘) n++; printf(„The array has %d elements.\n“, n);
int arr[5] = {10, 20, 30, 40}; int n = 0; while(arr[n] != ‚\0‘) n++; printf(„The array has %zu elements.\n“, n);	See above

Declaring a variable inside the for function

Not working	Working
for (int i=0; i<10;i++) { }	int i; for (i=0; i<10;i++) { }

Declaring a variable as an argument to a function

Not working	Working
int isPrime (unsigned int n) { }	unsigned int n; int isPrime (n) { }
has_space(s) char s[]; {	has_space(s) char *s; {

Type casting directly after the declaration

Not working	Working
char byte = (char) integer;	char byte; byte = (char) integer;

Explicitly declaring that a function returns no value

Not working	Working
void main (int)	main (int) /* or */ int main(int) /* for a function that returns an integer and takes an integer */
main() { int i; }	main() { int i; return; }

Variables of type const

Not working	Working
const int i = 10; const char *str;	int i = 10; /* or: #define INT 10 */ char *str;

Variables of type unsigned long

Not working	Working
unsigned long number;	long number; /* No format specifier %ul */ number = abs(number);

Using free() on a NULL initialized array

Not working	Working
int *arr = NULL; free (arr); /* This will crash the computer */	int *arr; arr=(int *)malloc(2*sizeof(int)); /* optional */ free (arr);

Declaring and initializing an array (a string) within a function

Not working	Working
int main(void) { char str[] = „Hello World!“; /* illegal assignment */ printf („%s\n“, str); return 0; }	char str[] = „Hello World!“; int main(void) { printf („%s\n“, str); return 0; } /* arrays must be declared as global */
char str[]; int main(void) { str = „Klingel“; /* illegal assignment */	char str[] = „Klingel“; int main(void) { printf(„Lastname: %s\n“, str);

Initializing a variable with a literal that ends with a data type suffix

Not working	Working
floatValue = 3.14f; longValue = 82787293729372L; unsignedIntValue = 10u;	floatValue = 3.14f; intValue = 12345; unsignedIntValue = 10;

Format conversion

Not working	Working
printf („float : %*f\n“, 3, 1.2345); printf („%0*d“, 5, 3); printf („int: %+d\n“, i); scanf („Number: %ld“, &n); printf(„integer: %i\n“, i); /* POWER C does not support the i, e, and p conversion types and does not understand the tab \t */	printf (float: %.3f\n“, 1.2345); /* POWER C does not use flags like ‚0‘ */ /* POWER C does not use flags like ‚+‘ */ scanf („Number: %d“, &n); printf(„integer: %d\n“, i); printf („pointer int: %d\n“, p);

Conversation from string to integer

Not working	Working
#include <stdlib.h> const char *str = „12345“; char *endptr; value = strtol(str, &endptr, 10);	/* No need to include stdlib.h! */ char str[] = „1234“; int main() { int num; num = atoi(str);

Automatic type casting

Not working	Working
int main() { int i; float f = 2.5; i = f; printf(„f: %f\ti: %f\n“, f, i); return(0); } /* In POWER C, i stays an integer and is not casted to a floating point */	int main() { int i = 2; float f; f = i; printf(„f: %f i: %d\n“, f, i); return(0); } /* In POWER C, only down casting works */

stdlib.h

Not working	Working
#include <stdlib.h>	/* POWER C has separate object files for i.e. free() and malloc(), which the linker will find when referenced */

Reading memory address

Not working	Working
volatile unsigned char *ptr = (volatile unsigned char *)0x800; unsigned char value = *ptr; printf („%c“, value);	unsigned int adr = 0x800; /* POWER C does not support the data type (volatile) unsigned char */ unsigned int *ptr = adr; printf („%u\n“, *(ptr)); /* dereference ptr */

Digraphs and trigraphs

Sys function

Inverting binary numbers

Not working	Working
t = ~t; /* The compiler will error out with „*** illegal use of ‚_'“, as the tidle ~ in the editor will be displayed to the compiler as an underscore _ */	Have not found a solution yet

Note that there is a typo on page 30 of the POWER C Instruction Manual from Spinnaker:

for ((c = getc(5)) != EOF)
  putchar(c);

Replace the „for“ with a „while“ statement to fix this.

Also, note that calling free( ) on a type that is not a pointer will halt your program und you have to press RUN/STOP to exit. Setting the variable to NULL does not help.

A char with the left-most bit set to 1 is always a positive value in POWER C:

int main() {
  char test = 255;
  printf("Test: %d\n", test);
  return(0);
}

Some CPU architectures (PDP-11, AMD x86 with GCC) would print -1 instead of 255 in above example. GCC would need the declaration „unsigned char test = 255“ to print the value 255.