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fgets ?

 
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Scottl



Joined: 21 Feb 2005
Posts: 25

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fgets ?
PostPosted: Mon Oct 22, 2007 4:58 pm     Reply with quote

I am using a PIC12F683 and trying to get the following code to work! Can someone tell what I am doing wrong. Anything I send to the pic it displays Test 88 never Test 6917.

#use rs232(baud=9600,parity=N,xmit=PIN_A1,rcv=PIN_A0,bits=8,STREAM=COM_A)
#use rs232(baud=9600,parity=N,xmit=PIN_A4,rcv=PIN_A5,bits=8,STREAM=COM_B)

Code:


void main()
{

char c[4];

while(1)
{

   fgets (c, COM_A);
   
   if (c == 6917)
   {
      fputs(c,COM_B);
      fprintf(COM_A, "Test 6917");
   }
   
   if (c == 88)
   {
      fprintf(COM_A, "Test 88"); 
   }
}



Thanks in advance,

Scott
rnielsen



Joined: 23 Sep 2003
Posts: 852
Location: Utah

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PostPosted: Mon Oct 22, 2007 5:11 pm     Reply with quote

First of all, this part does not have a hardware uart on board. If you are going to be inputing data to the PIC I would strongly suggest you use one with the hardware.

Next, you have defined your char variable 'c' to hold four bytes. You are trying to store four characters in it but you need a null character to specify the end of the string, ie a '0' (zero). You need to declare it: char c[5] to hold four characters plus the NULL.

It's fairly easy to use software uarts to transmit with but rather tricky to use them to receive data.

Search the forums on software uart and see what challenges others have stumbled upon.

Ronald
Scottl



Joined: 21 Feb 2005
Posts: 25

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PostPosted: Mon Oct 22, 2007 6:25 pm     Reply with quote

I have setup a test and everything works fine! All data sent comes back exact!

Code:


fgets (c, COM_A);
fprintf(COM_A, "%s", c);



All data is sent back perfectly!

I think the problem is with the following:

Code:


if (c==88)
{
   Do This!
}else{
   Do This! I type 88 but it always does this!
}



Do you see anything wrong with the my if statement?

Scott
Ttelmah
Guest







PostPosted: Tue Oct 23, 2007 4:16 am     Reply with quote

If you type '88', you send the two characters '8', and '8'. The single character, with the 'value' '88', is the letter 'X' (upper case).

Best Wishes
Scottl



Joined: 21 Feb 2005
Posts: 25

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PostPosted: Tue Oct 23, 2007 7:44 am     Reply with quote

Thanks Ttelmah!

This gets me everytime! Everything seems to be working fine.
Ttelmah
Guest







PostPosted: Tue Oct 23, 2007 8:44 am     Reply with quote

Yes, it is slightly confusing, especially if you are 'used' to languages, that allow a direct string comparison, and particularly if you are not 'used' to thinking about the numeric values that characters represent. After about the 500th error of this sort, you will find that you quite suddenly start to think in the right terms.... Smile

Best Wishes
Wayne_



Joined: 10 Oct 2007
Posts: 681

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PostPosted: Thu Oct 25, 2007 1:45 am     Reply with quote

Try the following:-

Asign a big enough buffer to allow for all incomming data
If you are sure you are only going to be recieving 4 bytes then DON't forget the null terminator as mentioned above so it would be c[5] as gets WILL put it on the end for you.

read up on strcmp and strstr. They return 0 for an EXACT match e.g.
"6917" == "6917" not "6917123"

char c[128];

while(1)
{

fgets (c, COM_A);

if (strcmp(c, "6917") == 0)
{
fputs(c,COM_B);
fprintf(COM_A, "Test 6917");
}

if (strcmp(c, "88") == 0)
{
fprintf(COM_A, "Test 88");
}
}
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