Function converting from 1-7 for days of the week to actual strings

**zx-1** · 01-01-2008

Originally Posted by stanlvw

I would love to use strftime but I'm afraid it's not supported in the C programming development suite that I'm using.

Your development suite doesn't support ISO standardized functions. So god only knows what else it's deficient in.

Probably a good idea to get a better development environment.

**stanlvw** · 01-01-2008

That's very likely what I'm doing for my next development project as I don't have time to start over again.

**stanlvw** · 01-01-2008

Below shows the code so far after some thinking and collaborations on getting around my problem.

Code:

// This function converts day of the week in number to string
void access_day(unsigned char number, char dayString[])
{
     // Declaration and Initialization of Days of the Week string
     char sundayArray[] = { 'S', 'u', 'n', 'd', 'a', 'y'};
     char mondayArray[] = { 'M', 'o', 'n', 'd', 'a', 'y'};
     char tuesdayArray[] = { 'T', 'u', 'e', 's', 'd', 'a', 'y'};
     char wednesdayArray[] = { 'W', 'e', 'd', 'n', 'e', 's', 'd', 'a', 'y'};
     char thursdayArray[] = { 'T', 'h', 'u', 'r', 's', 'd', 'a', 'y'};
     char fridayArray[] = { 'F', 'r', 'i', 'd', 'a', 'y'};
     char saturdayArray[] = { 'S', 'a', 't', 'u', 'r', 'd', 'a', 'y'};
     
     // index lookup table of the day strings
     /*uint indexArray[] = {&sundayArray, &mondayArray, &tuesdayArray,
                         &wednesdayArray, &thursdayArray, &fridayArray,
                         &saturdayArray};
     char* pDay = (char*) indexArray[0];*/
     
     char* pIndexArray[] = {&sundayArray, &mondayArray, &tuesdayArray,
                         &wednesdayArray, &thursdayArray, &fridayArray,
                         &saturdayArray};
     char* pDay = pIndexArray[number-1];
     
     
}

However, I'm wondering if I should make dayString a pointer instead of a char array and do this:

Code:

dayString = pIndexArray[number-1];

instead of:

Code:

char* pDay = pIndexArray[number-1];

to return the string of the actual day of the week rather than the number.

**zacs7** · 01-01-2008

You're not allowed to return a pointer to a local non-static variable (they'll be destroyed when the function is returned).

You're over complicating this way too much,

Code:

/* returns 0 on success, else non-zero */
int accessDay(size_t n, char * day, size_t maxLen)
{
    const char days[7][] = {    "Sunday"
                                "Monday",
                                "Tuesday",
                                "Wednesday",
                                "Thursday",
                                "Friday",
                                "Saturday"
                            };
                            
    /* adjust n, since it's 1 based */
    --n;
                            
    /* error day is out of bounds */
    if(n > (sizeof(days) / sizeof(days[0])))
        return 2;
    
    strncpy(day, days[n], maxLen);
    
    /* etc */
    
    return 0;
}

Of course, you'll still need to add error checking -- and it's not perfect either.

**Elysia** · 01-01-2008

Already did that.

**Elysia** · 01-01-2008

True enough, that does the trick.
A little mistake on iMalc's part, then, I guess. Proper C89 code would be:

Code:

void getDayOfWeekName(int inDayIndex, char *outDayName)
{
    static const char* const days[] =
        { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
    assert(1 <= inDayIndex && inDayIndex <= 7);
    assert(outDayName != NULL);
    strcpy(outDayName, days[inDayIndex - 1]);
}

**mike_g** · 01-01-2008

I dont know what asserts are but somehow this just looks wrong:

assert(1 <= inDayIndex && inDayIndex <= 7);

**whiteflags** · 01-01-2008

It's not. Just remove the assertion for a second and see for yourself:

Code:

#include <assert.h>
#include <stdio.h>
#include <string.h>

#define WYSIWYG(maybe) printf( #maybe##", %d\n", (maybe) );

void getDayOfWeekName( int inDayIndex, char *outDayName )
{
    static const char* const days[] =
        { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
     WYSIWYG( ( 1 <= inDayIndex && inDayIndex <= 7 ) )
    assert(outDayName != NULL);
    strcpy(outDayName, days[inDayIndex - 1]);
}

int main( void )
{
    int i;
    char p[10];

    for ( i = 1; i <= 7; i++ ) {
        getDayOfWeekName( i, p );
    }
    return 0;
}

**mike_g** · 01-01-2008

Oh yeah I'm dumb >_<

**iMalc** · 01-01-2008

Originally Posted by mike_g

I dont know what asserts are but somehow this just looks wrong:

I guess I confused things by putting that in there, and in the wrong place for C89.
I write it like this: 1 <= x && x <= 7 because it kinda looks like 1 <= x <= 7, which is pretty much mathematical syntax to show x being between 1 and 7 inclusive. Kinda nifty once you get used to it I think.
Feel free to write x >= 1 though instead of course.

**Codeplug** · 01-01-2008

My preference would be to return a const char*, for two reasons:
1) any need for an strcpy() is defered to the caller
2) ability to indicate a bad param error condition (return NULL)

gg

**Elysia** · 01-02-2008

I would also go with the return a const char* approach since it seems more flexible.
In many cases you might not want to reassign the actual string you get. You might want to compare it or such. Then a const char* is perfect.
However, if you really do need to modify the contents or use it in any way, you're free to do the copy yourself. Thus you may save time, as well. New function:

Code:

const char* getDayOfWeekName(int inDayIndex)
{
	static const char* const days[] = 
		{ "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
	assert(inDayIndex >= 1 && inDayIndex <= 7);
	return days[inDayIndex - 1];
}

**iMalc** · 01-02-2008

Yup that's good too IMHO.
Using const char* as the return value is useful.

**stanlvw** · 01-02-2008

Is the assertion used for error-checking to ensure that the number is within range? It seems that mikroC doesn't support that.

I came up with a way of getting around it such as:

Code:

const char* getDayOfWeekName(int inDayIndex)
{
        static const char* const days[] =
                { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday",
"Saturday" };
        if (!(inDayIndex >= 1 && inDayIndex <= 7)){
           return "Error";
        }
        return days[inDayIndex - 1];

}

Please let me know what you think. Thanks.

**iMalc** · 01-02-2008

assert is a debug-only check that breaks you into the debugger at the point where the statement was false.
On an embedded system I guess you'd need to implement your own form of assert, that perhaps just logs the error. What you've written could be fine for you.