Char Array questions

[eckcotech]

Hey all,

I have a small project that is pulling in an ADC value and converting it to a char string value with 8 bits....

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unsigned int myadc;
char adctxt[];
float aveadc;

myadc = ADC_Read(0);
aveadc = ((myadc * .6162) - 62.691);
FloatToStr(aveadc,adctxt);

This piece works great and is returning good results but they are formatted similar to this....

result = 51.58397

What i would like to do is get rid of anything beyond 2 decimal places and pad the number before the decimal to 3 places. something like this....

result = 051.58

I tried to do that by cycling through the array with the result in it and making decisions based on where the decimal landed. unfortunately, I have had no luck getting this to work as expected. Here's the code......

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if(adctxt[0]="."){
            retstr[0] = "0";
            retstr[1] = "0";
            retstr[2] = "0";
            retstr[3] = ".";
            retstr[4] = adctxt[1];
            retstr[5] = adctxt[2];
        }

        if(adctxt[1]="."){
            retstr[0] = "0";
            retstr[1] = "0";
            retstr[2] = adctxt[0];
            retstr[3] = ".";
            retstr[4] = adctxt[1];
            retstr[5] = adctxt[2];
        }
        
        if(adctxt[2]="."){
            retstr[0] = "0";
            retstr[1] = adctxt[0];
            retstr[2] = adctxt[1];
            retstr[3] = ".";
            retstr[4] = adctxt[2];
            retstr[5] = adctxt[3];
        }
        
        if(adctxt[3]="."){
            retstr[0] = adctxt[0];
            retstr[1] = adctxt[1];
            retstr[2] = adctxt[2];
            retstr[3] = ".";
            retstr[4] = adctxt[3];
            retstr[5] = adctxt[4];
        }

when I run this, it seems to print out garbage via the UART1_Write_Text(retstr).

Any ideas on what I might be doing wrong here??

[KaranSoin]

use sprintf() , it is designed for problems like this. The reason you are getting garbage is because size of adctxt[] is undefined, you are most likely overwriting the NULL terminating character at the end of the string.

Regards

[Mince-n-Tatties]

look up C string tools

memchr, you could use this to find the location of the decimal point in the array and work around that.

[Dany]

Code: Select all

char adctxt[];

Should this variable not be something like

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char adctxt[23];

to be capable of holding the string representation of a floating variable?
I think (but again I am no C guru), that

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char adctxt[];

only declared a pointer to a string and does not reservate space for the string itself.
All goes well until other some other variable is overwritten with the string contents.

Things like this should be taken up in the list "pitfalls for C programmers", if that existed.

This is only a side remark, it has no relation to the thread subject.

[Mince-n-Tatties]

Hi Dany,

Code: Select all

char adctxt[];

Should this variable not be something like

Code: Select all

char adctxt[23];

to be capable of holding the string representation of a floating variable?

[15] for the specific conversion library used.

Things like this should be taken up in the list "pitfalls for C programmers", if that existed.

mmm in the case of this exact topic side remark, this information already exist in the form of the user help manual "F1"