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nailuy
Joined: 21 Sep 2010
Posts: 159
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| it is possible to delete a string? |
 Posted: Mon May 02, 2016 10:10 am |
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Hy.
I try to renew string "J"
after using once function "strcmp", "J" have old data +new data.
question:
how can delete or renew string "J" after A=0?
| Code: | char I[] ={"test"};
/////////////////////////////////
A = strcmp ( I , J );
if (A==0)
{
printf(" %D ", A);
} |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 02, 2016 10:12 am |
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| Just set the first byte of the array to 0x00. This will "delete" the string. |
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nailuy
Joined: 21 Sep 2010
Posts: 159
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| Posted: Mon May 02, 2016 10:28 am |
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like this?
J[0]=0x00;
is not working.
| Code: | A = strcmp ( I , J );
if (A==0)
{
printf(" %D ", A);
J[0]=0x00;
} |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 02, 2016 10:44 am |
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How do you know it's not working ? Post the code that shows it's not
working. And tell me what you see when you run the code. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19548
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| Posted: Mon May 02, 2016 10:55 am |
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How do you know?.
Nothing you post shows what you then try to do with the string.
The _variable_ will still exist, but used as a string (so any of the string functions), it will then be an empty string.
Remember if this is inside a function, it'll be re-loaded whenever the function loads. Have switched this to I rather than J for a demo.
| Code: |
//Obviously suitable processor header, clock etc..
int1 demo(char * J)
{
char I[] ="test";
int1 A;
A = strcmp ( I , J );
if (A==0)
{
I[0]='\0';
}
return A;
}
//every time you call this, I[] will be reloaded with "test"
void main(void)
{
char test_compare[]="test"
if (demo(test_compare))
printf("Match\n");
else
printf("No match\n");
//will print "Match"
if (demo(test_compare))
printf("Match\n");
else
printf("No match\n");
//will printf "Match" again
}
//However if you change the declaration of demo to:
int1 demo(char * J)
{
static char I[] ="test";
int1 A;
A = strcmp ( I , J );
if (A==0)
{
I[0]='\0';
}
return A;
}
//It'll print "No match" the second time, as the variable is not re-loaded
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Using the second 'demo' version, the string gets cleared after the first match, and is not then reloaded (static declarations are only loaded once at the start), so the second call then does not match.
I see PCM_programmer posted exactly the same first line, while I was typing!...  |
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nailuy
Joined: 21 Sep 2010
Posts: 159
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| Posted: Mon May 02, 2016 10:59 am |
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I cant print entire code because is huge.
after J "test" is the same with I, show zero on display but with new "test" is not showing something else not even zero...
| Code: |
printf("%s ", J);
A = strcmp ( I , J );
if (A==0)
{
printf(" %D ", A);
J[0]=0x00;
} |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19548
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| Posted: Mon May 02, 2016 11:04 am |
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| strcmp, will return '0' for a match, or 1/-1 according to whether the strings are alphabetically less than or greater than each other. So 'of course' it'll return a non zero value. It'll no longer match.... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 02, 2016 11:04 am |
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Where is the code after you set J[0] = 0x00 ? That's the important
code, but you didn't show it.
Show the code where you use the J[] array, after the first byte is set to 0. |
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nailuy
Joined: 21 Sep 2010
Posts: 159
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| Posted: Mon May 02, 2016 11:15 am |
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this is the code after infinite loop
| Code: | if(kbhit()){
key = getc();
putc(key);
INDEX_COMAND=1;
if (key==13) //enter
{
printf("\r\n");
G=0;
J[0] = '\0';
}
}
if (key!=key2){
J[G]=key;
key2=key;
if (G<7){
G++;
}
printf("\r\n");
printf("%s ", J);
}
if (INDEX_COMAND<3)
{
INDEX_COMAND++;
if (INDEX_COMAND==2)
{
INDEX_COMAND=250;
COMP_COMAND = strcmp ( J , I );
if (COMP_COMAND==0) {
printf(" %D ", COMP_COMAND);
J[0] = '\0';
}
}
}
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 02, 2016 11:26 am |
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| Quote: |
G=0;
J[G]=key;
printf("%s ", J);
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After you do this, you have to make J[] into a string before you print it.
You have to write a 0x00 after the text bytes.
You have to do this:
| Quote: | G=0;
J[G]=key;
J[G+1] = 0x00;
printf("%s ", J); |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19548
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| Posted: Mon May 02, 2016 11:50 am |
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Just to explain.
In C, a 'string', is an array of characters _terminated with a NULL_ ('\0' or 0x00).
This is why you can 'clear' a string by putting a terminator at the start.
Your array needs a terminator.
Without this, the print will carry on printing stuff from memory, until it comes across a zero. So could be anything..... |
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nailuy
Joined: 21 Sep 2010
Posts: 159
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| Posted: Mon May 02, 2016 1:37 pm |
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Thank you for supplementary explanation.
As you say for printf is working but for strcmp is not working.
I'm interested for strcmp to work, printf is only for verifying.
What is happening?
Word is cleared when is "printed"
but after strcmp I have at:
one moment more 1's (because compaction f string)
single moment 0 (string are the same)
and -1 (string are not the same)
press enter
and again lot of 1's and nothing 0 or -1.
That's I'm saying is working half.
Can help me?
Thank you. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19548
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| Posted: Mon May 02, 2016 2:29 pm |
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Read what I posted earlier about strcmp.
strcmp, returns -1, 0, or 1 according to whether the first different character is greater than or less than the other. So '1' is a perfectly legitimate 'different' answer. How it would handle the first character being NULL, is arguable. It is actually better if this might ever be the case, to test this before calling strcmp (significantly quicker....). |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 02, 2016 2:33 pm |
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if strcmp() doesn't work, then add some debugging code to display both
strings in hex format. Look at the data that was printed. Make sure
the text has a 0x00 after the last text character. Make sure the text
is what you expected it to be in both strings. Example:
| Code: |
int8 index;
signed int8 result;
// Display the I string as hex bytes.
for(index = 0; index < sizeof(I); index++)
printf("%x ", I[index]);
printf("\n\r");
// Display the J string as hex bytes.
for(index = 0; index < sizeof(J); index++)
printf("%x ", J[i]);
printf("\n\r");
// Now do the string comparison.
result = strcmp(I, J);
printf("strcmp result = %d \n\r", result);
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nailuy
Joined: 21 Sep 2010
Posts: 159
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| Posted: Tue May 03, 2016 1:55 pm |
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yes PCM programmer thank you for your debugging solution.
I found where was the problem:
problem was because G are not making zero, are making 1 because after G=0 is G++ so when G=0 is placed where it should be placed code is working perfectly.
Ttelmah thank you for your support I read and applied your solution but I do not found where was the problem.
So you both had a support for me and thank you again so much for this.
Best regards |
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