String Parsing in C

It has been a while since I did some parsing in C, so I am trying to get it all back :o

I have a specific string that I need to parse. Basically get the specific string of length M starting at position X.

Here is a sample of data format:

Code:

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1  TestTeamCisco96279              68:7f:74:56:64:ec  WPA2PSK/AES            68      11b/g/n NONE  In

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I have a structure to to store this data.

Right now I have parse until WPAPSK/AES and I wanted to separate the string before and after "/" .

So here is what I did.

Code:

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int get_data(char *ssid, char *mac , char *auth, char * enc, const char *data)
{
char p[150];
char tmp[30];
 
 memset(p, 0, strlen(data) );
 memcpy(p, data, strlen(data));

 // get data starting at pos =57 length = 23
 memmove(tmp, p+57, 23);
 
 int pos = strcspn(tmp , "/");
 
  memmove(enc, tmp+pos+1, strlen(tmp)-pos);
  memmove(auth, p+57, pos);
 
 printf("Auth  :: %s \n", auth);
 printf("Encryption :: %s \n", enc);
}

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The output is these:

Code:

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Auth :: WPA2PSK
Encryption :: AES            WPA2PSK

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If I changed the lenght of Encryption to 10, then the data is corrrectly displayed.

This is something wrong with how I manipulated the pointers?

englighten me please :o

strcspn() works with null terminated strings.

But, there is no guarantee your strings are null terminated.

Code:

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memset(p, 0, strlen(data) );
memcpy(p, data, strlen(data));

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Let's suppose data is a string containing A, B, C, \0.
strlen() will return 3, not 4 because strlen does not take into account the last null character.
So memset(p, 0, strlen(data) ); will only write three zeros.
Then memcpy(p, data, strlen(data)); will only copy A, B, and C.
You end up with a string which is not null terminated.
A possible solution is simply:

Code:

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strcpy(p, data);

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you can you GNU Regular expressions Library

http://www.gnu.org/s/hello/manual/li...pressions.html

I don't know why you're using memcpy or memmove here. You could iterate the string looking for the slashes and use strncpy to extract the portion you want, you could use strtok to find the slashes, or you could use strstr to find the slashes and strncpy to extract the data between them.

@ olivthill2 , thanks for the tip. strcspn , gave me the correct position of the character. I was not able to include it in the post, but the temporary variable "tmp" was initialized using memset and its size is greater than the actual number of size I extracted from the original string, so I think "tmp" is null terminated. correct me if am wrong. :o

@aamir121a , thanks for the suggestion. I was actually looking at it too. I am making this program on a busybox so there is very limited libraries and functions available. I am not sure if regular expression included in the platform. I will check.

@GCDEF .. strtok works its wonders again. thanks.

thank you all for the suggestions. :wave: