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Double sscanf confilicts, overwrites over variables

Hi

When I run this code it overwrites second parameter over first ones:

unsigned char test1[4];
unsigned char test2[4];
memset(test1, 0, 4);
sscanf(param2, "%d.%d.%d.%d", &(test1[0]), &(test1[1]), &(test1[2]), &(test1[3]));
memset(test2, 0, 4);
sscanf(param1, "%d.%d.%d.%d", &(test2[0]), &(test2[1]), &(test2[2]), &(test2[3]));


When I debug, when I reach sscanf sscanf(param2...) it parses test1 properly and I have proper data in test1

When I reach and finish execution of scanf(param1...) it overwrites data and makes test1 data 0

Please advice.
Thanks from now
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CSecurity
Asked:
CSecurity
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1 Solution
 
Infinity08Commented:
%d reads an integer value. You only provide room for one char. The size of an int is typically bigger than that of a char (often 4 times as big).

Either you want to read characters, and then you should use %c instead of %d, or you want to read integer values, and then you should provide enough room for an int.
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CSecurityAuthor Commented:
it's IP address, %c not works but %d works... and it fits... Just when I call it second time just 2 lines below it corrupts previous data
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Infinity08Commented:
Did you understand what I meant in my previous post ?

%d will write 4 bytes (typically), not just 1 byte as you want it to. You'll need to either read them into 4 ints rather than 4 chars, or you'll have to read and process the 4 values one by one.
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CSecurityAuthor Commented:
>> read and process the 4 values one by one.

How?

reading them in 4 chars is not a case
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CSecurityAuthor Commented:
>> read and process the 4 values one by one.

How?

reading them in 4 ints is not a case
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Infinity08Commented:
You read an int, and cast it to an unsigned char.
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Infinity08Commented:
>> It's your code

Heh, got me ;)

But, why not use inet_pton, which was my first suggestion ?
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CSecurityAuthor Commented:
>> Heh, got me ;)
:-)

>> But, why not use inet_pton, which was my first suggestion ?
I want to use something like sscanf or alternatives to that, I don't want to include a lib, I need just a function or a piece of code
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CSecurityAuthor Commented:
Also I should mention again that it works first time, when I re-call it just 2 lines below, it overwrites bytes above... But for first time, it works properly
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Infinity08Commented:
Try something like this instead :
const char *ip_addr = "192.168.0.1";
unsigned char ip[4] = { 0 };
unsigned int tmp[4] = { 0 };
if (4 == sscanf(ip_addr, "%u.%u.%u.%u", &(tmp[0]), &(tmp[1]), &(tmp[2]), &(tmp[3]))) {
  int i = 0;
  for (i = 0; i < 4; ++i) {
    ip[i] = (unsigned char) tmp[i];
  }
}
else {
  // error parsing the IP address !!
}

Open in new window

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Infinity08Commented:
>> But for first time, it works properly

That's because of endianness. Your platform is apparently little endian ... But it's dangerous code, since you're writing past the end of the buffer (3 bytes past it to be exact), thus overwriting memory that doesn' t belong to the buffer.

If you'll only run this code on a little endian system with 32bit integers, you can still use my original code (from the previous question), as long as you increase the buffer size to 7 bytes instead of 4.
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CSecurityAuthor Commented:
Thank you so much!
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Infinity08Commented:
I've got to go now, but I'll be back in a few hours if there are further questions/problems.
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CSecurityAuthor Commented:
Code works properly, thank you so much
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