Strange problem with sprintf function in CCS4 compiler

[scorrpeio]

Hello,

I have variables in float which I am interested in converting to char array.
For this I used sprintf function and enabled full support to library functions in Code Composer Studio 4.

//global declaration
// Struct_Parameters_RunMode.f32TotalisedFlow is a float type in a structure
UINT8_T  G_u8TotalisedFlow_ASCII[13]	= {0,0,0,0,0,0,0,0,0,0,0,0,0};
UINT8_T   G_u8Size_Totalised		= 0;

Struct_Parameters_RunMode.f32TotalisedFlow = 1234506789;
	sprintf( (UINT8_T*)G_u8TotalisedFlow_ASCII, "%.0f", Struct_Parameters_RunMode.f32TotalisedFlow );
	while(G_u8TotalisedFlow_ASCII[G_u8Size_Totalised]!= DEF_NULL )
	{
	 	G_u8Size_Totalised++;
	}

when I see the output of this piece of code
I see like this ...

G_u8TotalisedFlow_ASCII[13]	= {'1','2','3','4','5','0','6','7','9','2'};

I dont understand why is this happening.
If I give a value less than 8 digits (12345678) I get desired output.

I have made stack size 1000bytes and heap size 960 bytes. I think, this is sufficient for sprintf function.

Please let me know, how to resolve this issue.

 

[FvM]

I guess you'll want to think about resolution of float variables in terms of exact decimal digits.

 

[scorrpeio]

Actually, if no of digits in float variable exceeds 8 (i.e. value greater than 9999999) sprintf can't retrieve the accurate char array equivalent to that float value.
That is where I am looking into as why would this happen?

- - - Updated - - -

1234506789 is what I am passing to sprintf and 1234506792 is what I am retrieving in char array.

 

[FvM]

The highest number that can be represented in float without possible truncation errors is 2^24 - 1. Above this limit, some numbers may be still correct by chance.

 

[scorrpeio]

Okay....
this explains why am I getting an erroneous value.
So, I will have to write my own "number to char" function.
Any reference of how to convert float value to char?

 

[madhusuthanan]

hi,

before sprintf all numbers as converted to string then you can receive as string.