read int(long) from a file

[Lingyun Yang]

Dear all,

I have a file it's binary data viewed in UltraEdit is
EF BB BF 0D 0A 3C .......
I want to read them into a int or long int array byte[]
for example:
byte[0]=0xEFBB
byte[1]=0xBF0D

I write the following code, but the output isn't right:

/* ---------------code --------------- */

char dictfilename[256]="test.txt";
FILE *dictfile;
struct stat stats;

dictfile = fopen(dictfilename,"rb");
if (stat (dictfilename, &stats) == -1)
{
printf("dict file not exist!\n");
return 0;
}

int buffer[256]={1,2,3,4,5,6,7,8,9};

fread (buffer, sizeof(int), 256, dictfile);
fclose (dictfile);
for(int i=0; i<16; ++i)
printf("0xd%",buffer);

/* ---------- end of the code ---------- */

the output is :
0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd

Is my code right?
It seems fread didn't read anything into buffer[]

Thank you for your help!


Lingyun Yang

 

[Martin Ambuhl]

Dear all,

I have a file it's binary data viewed in UltraEdit is
EF BB BF 0D 0A 3C .......
I want to read them into a int or long int array byte[]
for example:
byte[0]=0xEFBB
byte[1]=0xBF0D

I write the following code, but the output isn't right:

/* ---------------code --------------- */

char dictfilename[256]="test.txt";
FILE *dictfile;
struct stat stats;

dictfile = fopen(dictfilename,"rb");
if (stat (dictfilename, &stats) == -1)
{
printf("dict file not exist!\n");
return 0;
}

int buffer[256]={1,2,3,4,5,6,7,8,9};

fread (buffer, sizeof(int), 256, dictfile);
fclose (dictfile);
for(int i=0; i<16; ++i)
printf("0xd%",buffer);

/* ---------- end of the code ---------- */

the output is :
0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd0xd

Is my code right?

No. Hell, it isn't even compilable. And even if you turn it into a
program, stat() is not a standard function. Here's some code for you to
play with:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
FILE *inout;
const unsigned char outdata[] =
{ 0xef, 0xbb, 0xbf, 0x0d, 0x0a, 0x3c };
/* Any of the following may lead to a zero-size array, which is not
legal C. I could do the checks at runtime, but I have left the
possibly illegal code, with a chicken-ass runtime check. */
unsigned short xshrt[sizeof outdata / sizeof(short)];
unsigned long xlong[sizeof outdata / sizeof(long)];
unsigned long long xllng[sizeof outdata / sizeof(long long)];
size_t i, Transfered;

if (!(inout = fopen("testdata", "wb"))) {
printf("could not open 'testdata' for outout\n");
exit(EXIT_FAILURE);
}

Transfered =
fwrite(outdata, sizeof *outdata,
sizeof outdata / sizeof *outdata, inout);
printf("Output transfer was %lu units of %lu bytes (wanted %lu)\n",
(unsigned long) Transfered, (unsigned long) sizeof *outdata,
(unsigned long) (sizeof outdata / sizeof *outdata));
fclose(inout);

if (sizeof outdata != sizeof xshrt) {
printf("There is a problem with reading into shorts.\n");
exit(EXIT_FAILURE);
}
if (!(inout = fopen("testdata", "rb"))) {
printf("could not open 'testdata' for outout\n");
exit(EXIT_FAILURE);
}
Transfered =
fread(xshrt, sizeof *xshrt,
sizeof xshrt / sizeof *xshrt, inout);
printf("Input transfer was %lu units of %lu bytes (wanted %lu)\n",
(unsigned short) Transfered, (unsigned short) sizeof *xshrt,
(unsigned short) (sizeof xshrt / sizeof *xshrt));
fclose(inout);
printf("Unsigned shorts: ");
for (i = 0; i < sizeof xshrt / sizeof *xshrt; i++)
printf("%#hx ", (unsigned short) xshrt);
printf("\n\n");

if (sizeof outdata != sizeof xlong) {
printf("There is a problem with reading into longs.\n");
exit(EXIT_FAILURE);
}
if (!(inout = fopen("testdata", "rb"))) {
printf("could not open 'testdata' for outout\n");
exit(EXIT_FAILURE);
}
Transfered =
fread(xlong, sizeof *xlong,
sizeof xlong / sizeof *xlong, inout);
printf("Input transfer was %lu units of %lu bytes (wanted %lu)\n",
(unsigned long) Transfered, (unsigned long) sizeof *xlong,
(unsigned long) (sizeof xlong / sizeof *xlong));
fclose(inout);
printf("Unsigned shorts: ");
for (i = 0; i < sizeof xlong / sizeof *xlong; i++)
printf("%#lx ", xlong);
printf("\n\n");


if (sizeof outdata != sizeof xllng) {
printf("There is a problem with reading into long longs.\n");
exit(EXIT_FAILURE);
}
if (!(inout = fopen("testdata", "rb"))) {
printf("could not open 'testdata' for outout\n");
exit(EXIT_FAILURE);
}
Transfered =
fread(xllng, sizeof *xllng,
sizeof xllng / sizeof *xllng, inout);
printf("Input transfer was %lu units of %lu bytes (wanted %lu)\n",
(unsigned long long) Transfered,
(unsigned long long) sizeof *xllng,
(unsigned long long) (sizeof xllng / sizeof *xllng));
fclose(inout);
printf("Unsigned shorts: ");
for (i = 0; i < sizeof xllng / sizeof *xllng; i++)
printf("%#llx ", xllng);
printf("\n\n");


return 0;
}

[output]
Output transfer was 6 units of 1 bytes (wanted 6)
Input transfer was 3 units of 2 bytes (wanted 3)
Unsigned shorts: 0xbbef 0xdbf 0x3c0a

There is a problem with reading into longs.

 

[Martin Ambuhl]

Martin Ambuhl wrote [code that had many typos and errors]

Please ignore that code, except, possibly, to fix it. I have sent a
cancel, but those are largely ignored since the days of the rogue cancelbots.

 

[Emmanuel Delahaye]

Dear all,

I have a file it's binary data viewed in UltraEdit is
EF BB BF 0D 0A 3C .......
I want to read them into a int or long int array byte[]

It makes a difference. Be more informative.

The id 'byte' is inappropriate here. A 'byte' is the smallest addressable
amount of memory for a given platform.

for example:
byte[0]=0xEFBB
byte[1]=0xBF0D

I write the following code, but the output isn't right:

Your code is very broken.

/* ---------------code --------------- */

Assuming a wrapper such as:

#include <stdio.h>
int main (void)
{
....
return 0;
}

char dictfilename[256]="test.txt";

Why do you waste so many bytes for a simple string literal?

static char const dictfilename[] = "test.txt";

FILE *dictfile;
struct stat stats;

This is not standard C.

dictfile = fopen(dictfilename,"rb");
if (stat (dictfilename, &stats) == -1)

The standard basic way is:

if (dictfile == NULL)

{
printf("dict file not exist!\n");
return 0;

0 means 'OK'. Better to use EXIT_FAILURE...

}

int buffer[256]={1,2,3,4,5,6,7,8,9};

Why in the world do you need to initialize this array? Debug purpose?

fread (buffer, sizeof(int), 256, dictfile);

It's important to store and test the returned value. It gives indications
about the reading operation results. Open your C-book for details.

fclose (dictfile);
for(int i=0; i<16; ++i)
printf("0xd%",buffer);

This is very bad. You need to read your C-book more carefully:

{
printf ("0x%X ", (unsigned) buffer);
}
printf ("\n");

I see what you intend to do. Be careful that the binary representation of
objetcts bigger than a byte may change from an implementation to another. It
means that you file can have the following bytes :

0x12 0x34

but once read and converted 'rawly', you can obtain:

0x1234
0x0001234
0x3412
0x34120000
etc. which are all different. Details belongs to your platform (endianness,
data width etc.)

Nota that some implementations supply 'hton()' 'or 'ntoh()' family functions
to convert properly the data (assuming h = host and n = network, hence MSB
first)

/* ---------- end of the code ---------- */

Try this, but be careful, as explained above, the result is not portable.

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main (void)
{
int ret;
static char const dictfilename[] = "test.txt";
FILE *dictfile = fopen (dictfilename, "rb");

if (dictfile == NULL)
{
if (errno)
{
perror (dictfilename);
}
ret = EXIT_FAILURE;

#if 0
/* to make the binary file if not exists... */
{
char buffer[] =
{0xEF, 0xBB, 0xBF, 0x0D, 0x0A, 0x3C};

FILE *dictfile = fopen (dictfilename, "wb");
size_t i;

for (i = 0; i < sizeof buffer; i++)
{
fputc (buffer, dictfile);
}
fclose (dictfile);
}
#endif
}
else
{
int buffer[256] =
{1, 2, 3, 4, 5, 6, 7, 8, 9};

int n = fread (buffer
,sizeof *buffer
,sizeof buffer / sizeof *buffer
,dictfile);

if (feof (dictfile))
{
printf ("EOF\n");
}

if (ferror (dictfile))
{
if (errno)
{
perror (dictfilename);
}
ret = EXIT_FAILURE;
}
else
{
ret = EXIT_SUCCESS;
}

fclose (dictfile);

{
int i;
for (i = 0; i < n; ++i)
{
printf ("%04X ", (unsigned) buffer);
}
printf ("\n");
}
}
return ret;
}

<Borland C 3.1 (16-bit)>

D:\CLC\Y\YANG>bc proj.prj
EOF
BBEF 0DBF 3C0A

</>

 

[Lingyun Yang]

Thank you for your help.
I am a newbie in C.
as you said I should open my C-book and study carefully

Dear all,

I have a file it's binary data viewed in UltraEdit is
EF BB BF 0D 0A 3C .......
I want to read them into a int or long int array byte[]

It makes a difference. Be more informative.

The id 'byte' is inappropriate here. A 'byte' is the smallest addressable
amount of memory for a given platform.

for example:
byte[0]=0xEFBB
byte[1]=0xBF0D

I write the following code, but the output isn't right:

Your code is very broken.

/* ---------------code --------------- */

Assuming a wrapper such as:

#include <stdio.h>
int main (void)
{
...
return 0;
}

char dictfilename[256]="test.txt";

Why do you waste so many bytes for a simple string literal?

static char const dictfilename[] = "test.txt";

FILE *dictfile;
struct stat stats;

This is not standard C.

dictfile = fopen(dictfilename,"rb");
if (stat (dictfilename, &stats) == -1)

The standard basic way is:

if (dictfile == NULL)

{
printf("dict file not exist!\n");
return 0;

0 means 'OK'. Better to use EXIT_FAILURE...

}

int buffer[256]={1,2,3,4,5,6,7,8,9};

Why in the world do you need to initialize this array? Debug purpose?

fread (buffer, sizeof(int), 256, dictfile);

It's important to store and test the returned value. It gives indications
about the reading operation results. Open your C-book for details.

fclose (dictfile);
for(int i=0; i<16; ++i)
printf("0xd%",buffer);

This is very bad. You need to read your C-book more carefully:

{
printf ("0x%X ", (unsigned) buffer);
}
printf ("\n");

I see what you intend to do. Be careful that the binary representation of
objetcts bigger than a byte may change from an implementation to another. It
means that you file can have the following bytes :

0x12 0x34

but once read and converted 'rawly', you can obtain:

0x1234
0x0001234
0x3412
0x34120000
etc. which are all different. Details belongs to your platform (endianness,
data width etc.)

Nota that some implementations supply 'hton()' 'or 'ntoh()' family functions
to convert properly the data (assuming h = host and n = network, hence MSB
first)

/* ---------- end of the code ---------- */

Try this, but be careful, as explained above, the result is not portable.

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main (void)
{
int ret;
static char const dictfilename[] = "test.txt";
FILE *dictfile = fopen (dictfilename, "rb");

if (dictfile == NULL)
{
if (errno)
{
perror (dictfilename);
}
ret = EXIT_FAILURE;

#if 0
/* to make the binary file if not exists... */
{
char buffer[] =
{0xEF, 0xBB, 0xBF, 0x0D, 0x0A, 0x3C};

FILE *dictfile = fopen (dictfilename, "wb");
size_t i;

for (i = 0; i < sizeof buffer; i++)
{
fputc (buffer, dictfile);
}
fclose (dictfile);
}
#endif
}
else
{
int buffer[256] =
{1, 2, 3, 4, 5, 6, 7, 8, 9};

int n = fread (buffer
,sizeof *buffer
,sizeof buffer / sizeof *buffer
,dictfile);

if (feof (dictfile))
{
printf ("EOF\n");
}

if (ferror (dictfile))
{
if (errno)
{
perror (dictfilename);
}
ret = EXIT_FAILURE;
}
else
{
ret = EXIT_SUCCESS;
}

fclose (dictfile);

{
int i;
for (i = 0; i < n; ++i)
{
printf ("%04X ", (unsigned) buffer);
}
printf ("\n");
}
}
return ret;
}

<Borland C 3.1 (16-bit)>

D:\CLC\Y\YANG>bc proj.prj
EOF
BBEF 0DBF 3C0A

</>

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