C’de floating point

Aralık 12, 2011 § Yorum yok § Kalıcı bağlantı

Floating point karşılaştırması kesin midir?

#include <stdio.h>

int main()
        float f=0.0f;
        int i;

                f = f + 0.1f;

        if(f == 1.0f)
                printf("f is 1.0 \n");
                printf("f is NOT 1.0\n");

        return 0;

Böyle bir karşılaştırma yerine şöle bir karşılaştırma kullanalım…

#include <stdio.h>

int main()
        float f=0.0f;
        int i;

                f = f + 0.1f;

        if ((f-1.0f)<0.00000000001f)
                printf("f is 1.0 \n");
                printf("f is NOT 1.0\n");

        return 0;

C’de sleep etkisi?

Aralık 12, 2011 § Yorum yok § Kalıcı bağlantı

Bak şu sleep’in yaptığına!

Sizce aşağıdaki program ne döner???

 #include <stdio.h>
  #include <unistd.h>
  int main()
          return 0;

Rest in Peace Dennis!

Ekim 16, 2011 § Yorum yok § Kalıcı bağlantı

#include stdio.h

int main()
    printf("goodbye, dad\n");
    return 0;

“UNIX is very simple, it just needs a genius to understand its simplicity.”
Dennis Ritchie

Rest in peace GREAT MAN!

gdb c debugger kullanımı

Ağustos 17, 2011 § 1 yorum § Kalıcı bağlantı

Programı yazalım

$ vim factorial.c
# include <stdio.h>

int main()
	int i, num, j;
	printf ("Enter the number: ");
	scanf ("%d", &num );

	for (i=1; i<num; i++)

	printf("The factorial of %d is %d\n",num,j);
$ cc factorial.c

$ ./a.out
Enter the number: 3
The factorial of 3 is 12548672

gdb kullanabilmek için ”cc -g” ile compile edelim

$ cc -g factorial.c

Önce gdb yi a.out için çalıştırıyoruz.

$ gdb a.out

Sonra break point koyuyoruz


break line_number

      break [file_name]:line_number
      break [file_name]:func_name

break 10
Breakpoint 1 at 0x804846f: file factorial.c, line 10.

“run ” ile programı çalıştır

run [args]

Starting program: /home/sathiyamoorthy/Debugging/c/a.out

İlk break pointe kadar program çalışır eder

Breakpoint 1, main () at factorial.c:10
10			j=j*i;

Bu noktada debug edebiliriz
Değişken değerlerine bakalım

Syntax: print {variable}

print i
print j
print num

(gdb) p i
$1 = 1
(gdb) p j
$2 = 3042592
(gdb) p num
$3 = 3

gdb ile kullanılabilecek diğer seçenekler
c (continue kısaltması): Bir sonraki break point e kadar sür.
n (next kısaltması): Birsonraki satırı sür
s (step kısaltması): n ile aynıdır fakat fonksiyon geldiğinde fonksiyonu tek satır olarak almaz fonksiyona gidip onu satır satır çalıştırır

Diğer seçeekler
l – list
p – print
c – continue
s – step
ENTER: bir önceki emri tekrar et
l command: Kaynak kodu görmek için kullanılır
bt: backtrack – Print backtrace of all stack frames, or innermost COUNT frames.
help – help TOPICNAME.
quit – çıkış


C’de hataları yakalamak

Temmuz 21, 2011 § Yorum yok § Kalıcı bağlantı

  • In C programming language, there is an external variable called “errno”.
  • From this errno variable you can use some error handling functions to find out the error description and handle it appropriately.
  • You have to include errno.h header file to use external variable errno.
    perror function prints error description in standard error.
  • The strerror function returns a string describing the error code passed in the argument errnum.

The following C code snippet tries to open a file through open system call. There are two flags in the open call. O_CREAT flag is to create a file, if the file does not exist. O_EXCL flag is used with O_CREAT, if the file is already exist open call will fail with the proper error number.

cat fileopen.c
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
// Declaration of a file descriptor
int fd;
// Opening a file
fd = open("/root/sasikala/testing",O_CREAT|O_EXCL);
// If Open is failed
if ( fd < 0 ) {
        printf("Opening file : Failed\n");
        printf ("Error no is : %d\n", errno);
        printf("Error description is : %s\n",strerror(errno));
// If Open is success
        printf("Opening file : Success\n");

$ cc -o fileopen fileopen.c
$ ./fileopen
Opening file : Success
$ ./fileopen
Opening file : Failed
Error no is : 17
Error description is : File exists
Error number Error Code Error Description
1 EPERM Operation not permitted
2 ENOENT No such file or directory
3 ESRCH No such process
4 EINTR Interrupted system call
5 EIO I/O error
6 ENXIO No such device or address
7 E2BIG Argument list too long
8 ENOEXEC Exec format error
9 EBADF Bad file number
10 ECHILD No child processes
11 EAGAIN Try again
12 ENOMEM Out of memory
13 EACCES Permission denied
14 EFAULT Bad address
15 ENOTBLK Block device required
16 EBUSY Device or resource busy
17 EEXIST File exists
18 EXDEV Cross-device link
19 ENODEV No such device
20 ENOTDIR Not a directory
21 EISDIR Is a directory
22 EINVAL Invalid argument
23 ENFILE File table overflow
24 EMFILE Too many open files
25 ENOTTY Not a typewriter
26 ETXTBSY Text file busy
27 EFBIG File too large
28 ENOSPC No space left on device
29 ESPIPE Illegal seek
30 EROFS Read-only file system
31 EMLINK Too many links
32 EPIPE Broken pipe
33 EDOM Math argument out of domain of func
34 ERANGE Math result not representable
35 EDEADLK Resource deadlock would occur
36 ENAMETOOLONG File name too long
37 ENOLCK No record locks available
38 ENOSYS Function not implemented
39 ENOTEMPTY Directory not empty
40 ELOOP Too many symbolic links encountered
42 ENOMSG No message of desired type
43 EIDRM Identifier removed
44 ECHRNG Channel number out of range
45 EL2NSYNC Level 2 not synchronized
46 EL3HLT Level 3 halted
47 EL3RST Level 3 reset
48 ELNRNG Link number out of range
49 EUNATCH Protocol driver not attached
50 ENOCSI No CSI structure available
51 EL2HLT Level 2 halted
52 EBADE Invalid exchange
53 EBADR Invalid request descriptor
54 EXFULL Exchange full
55 ENOANO No anode
56 EBADRQC Invalid request code
57 EBADSLT Invalid slot
59 EBFONT Bad font file format
60 ENOSTR Device not a stream
61 ENODATA No data available
62 ETIME Timer expired
63 ENOSR Out of streams resources
64 ENONET Machine is not on the network
65 ENOPKG Package not installed
66 EREMOTE Object is remote
67 ENOLINK Link has been severed
68 EADV Advertise error
69 ESRMNT Srmount error
70 ECOMM Communication error on send
71 EPROTO Protocol error
72 EMULTIHOP Multihop attempted
73 EDOTDOT RFS specific error
74 EBADMSG Not a data message
75 EOVERFLOW Value too large for defined data type
76 ENOTUNIQ Name not unique on network
77 EBADFD File descriptor in bad state
78 EREMCHG Remote address changed
79 ELIBACC Can not access a needed shared library
80 ELIBBAD Accessing a corrupted shared library
81 ELIBSCN .lib section in a.out corrupted
82 ELIBMAX Attempting to link in too many shared libraries
83 ELIBEXEC Cannot exec a shared library directly
84 EILSEQ Illegal byte sequence
85 ERESTART Interrupted system call should be restarted
86 ESTRPIPE Streams pipe error
87 EUSERS Too many users
88 ENOTSOCK Socket operation on non-socket
89 EDESTADDRREQ Destination address required
90 EMSGSIZE Message too long
91 EPROTOTYPE Protocol wrong type for socket
92 ENOPROTOOPT Protocol not available
93 EPROTONOSUPPORT Protocol not supported
94 ESOCKTNOSUPPORT Socket type not supported
95 EOPNOTSUPP Operation not supported on transport endpoint
96 EPFNOSUPPORT Protocol family not supported
97 EAFNOSUPPORT Address family not supported by protocol
98 EADDRINUSE Address already in use
99 EADDRNOTAVAIL Cannot assign requested address
100 ENETDOWN Network is down
101 ENETUNREACH Network is unreachable
102 ENETRESET Network dropped connection because of reset
103 ECONNABORTED Software caused connection abort
104 ECONNRESET Connection reset by peer
105 ENOBUFS No buffer space available
106 EISCONN Transport endpoint is already connected
107 ENOTCONN Transport endpoint is not connected
108 ESHUTDOWN Cannot send after transport endpoint shutdown
109 ETOOMANYREFS Too many references: cannot splice
110 ETIMEDOUT Connection timed out
111 ECONNREFUSED Connection refused
112 EHOSTDOWN Host is down
113 EHOSTUNREACH No route to host
114 EALREADY Operation already in progress
115 EINPROGRESS Operation now in progress
116 ESTALE Stale NFS file handle
117 EUCLEAN Structure needs cleaning
118 ENOTNAM Not a XENIX named type file
119 ENAVAIL No XENIX semaphores available
120 EISNAM Is a named type file
121 EREMOTEIO Remote I/O error
122 EDQUOT Quota exceeded
123 ENOMEDIUM No medium found
124 EMEDIUMTYPE Wrong medium type
125 ECANCELED Operation Canceled
126 ENOKEY Required key not available
127 EKEYEXPIRED Key has expired
128 EKEYREVOKED Key has been revoked
129 EKEYREJECTED Key was rejected by service
130 EOWNERDEAD Owner died
131 ENOTRECOVERABLE State not recoverable

Neredeyim ben!?

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