|  | reading byte by byte from memory | | |
| | | Ashit Vora |  |
|  Posted: Sat Sep 06, 2008 4:55 am Post subject: reading byte by byte from memory |  |
Hi,
I had one small query.
I 'm coping data from an unsigned short to a char*.
code is
#include<stdio.h>
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
memset(buf,0,512);
//copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
}
here, how to I cehck if the data has been successfully copied or not.
the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
At server I wanna check if the value received is 0xFE10 pr not.
Can anyone please help me with this? 'm new to memory level C prog.
Thanks in advance. |
| |
| | | Martin Ambuhl | |
| | Posted: Sat Sep 06, 2008 4:55 am Post subject: Re: reading byte by byte from memory | |
| |  | |
Ashit Vora wrote:
| Quote: | Hi,
I had one small query.
|
You should stop asking and start reading.
| Quote: | I 'm coping data from an unsigned short to a char*.
|
No you are not.
You have been told about <stdlib.h>, but you're too damn smart to listen.
| Quote: |
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
^^^^^^^ |
Not only is this a gross error, but if it had actually been a legal cast
it would have been stupid. You have been told this, and you have been
told why, but you're too damn smart to listen.
| Quote: | memset(buf,0,512);
|
You also should know better than hard-coding constants like 512.
| Quote: | //copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
^^^^ ^^^ |
(1) (2)
(1) type is an unsigned short. The second argument to memcpy is a
pointer-to-void. Did you ever bother even looking at the description of
memcpy.
(2) If you're going to make implementation-specific assumptions about,
for example, byte order, you are on your own. There is no reason to
think that copying two bytes
| Quote: | }
here, how to I cehck if the data has been successfully copied or not.
|
Of course, it hasn't. Don't be such a fool.
| Quote: | the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
|
You have no business trying to write code. You haven't learned a damn
thing either from the replies to your previous questions or from the
programming course that you obviously failed,
| Quote: | At server I wanna check if the value received is 0xFE10 pr not.
Can anyone please help me with this? 'm new to memory level C prog.
No one can help you, since you ignore everything people tell you. |
|
| |
| | | CBFalconer | |
| | Posted: Sat Sep 06, 2008 4:55 am Post subject: Re: reading byte by byte from memory | |
Martin Ambuhl wrote:
| Quote: | Ashit Vora wrote:
.... snip ...
here, how to I cehck if the data has been successfully copied or not.
Of course, it hasn't. Don't be such a fool.
the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
You have no business trying to write code. You haven't learned a damn
thing either from the replies to your previous questions or from the
programming course that you obviously failed,
At server I wanna check if the value received is 0xFE10 pr not.
Can anyone please help me with this? 'm new to memory level C prog.
No one can help you, since you ignore everything people tell you.
|
I gather you don't consider his code exemplary? :-)
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section. |
| |
| | | Ashit Vora | |
| | Posted: Sat Sep 06, 2008 5:10 am Post subject: Re: reading byte by byte from memory | |
| | | |
On Sep 5, 9:55 pm, Ashit Vora <a.k.v...@gmail.com> wrote:
| Quote: | Hi,
I had one small query.
I 'm coping data from an unsigned short to a char*.
code is
#include<stdio.h
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
memset(buf,0,512);
//copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
}
here, how to I cehck if the data has been successfully copied or not.
the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
At server I wanna check if the value received is 0xFE10 pr not.
Can anyone please help me with this? 'm new to memory level C prog.
Thanks in advance.
|
Here is the actual code 'm using... If it makes the picture more
clear.
Client's piece of code.
//total_buf_size is the sum of header plus data
total_buf_size=10;
buf =(char*) malloc (total_buf_size);
if(buf==NULL){
printf("Malloc Failed\n");
}
memset(buf,0, total_buf_size);
memcpy(buf,&type,2);
memcpy(&buf[2],&offset,4);
memcpy(&buf[6],&data_length,4);
/*now sending the data BYTE AT A TIME*/
for(i=0;i<10;i++){
if(send(client_sock,&buf[i],1,0)==-1){
perror("send");
exit(1);
}
}
/**************************************************/
Server's piece of Code is:
for(i=0;i<10;i++){
if(recv(new_fd,&buf[i],1, 0)==-1){
perror("receive");
exit(1);
}
printf("%02x \t",buf[i]);
}
printf("\n");
memcpy(&type,buf,2);
buf+=2;
memcpy(&offset,buf,4);
buf+=4;
memcpy(&data_length,buf,4);
printf("TYPE: %s\n",(char*)type);
if(type == 0xFE10)
printf("RECEIVED");
else
printf("NOT RECEIVED");
}
NOTE: type at client was unsigned short type=0xFE10
Thanks |
| |
| | | pete | |
| | Posted: Sat Sep 06, 2008 5:14 am Post subject: Re: reading byte by byte from memory | |
| | | |
Ashit Vora wrote:
| Quote: | Hi,
I had one small query.
I 'm coping data from an unsigned short to a char*.
code is
#include<stdio.h
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
memset(buf,0,512);
//copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
}
here, how to I cehck if the data has been successfully copied or not.
the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
At server I wanna check if the value received is 0xFE10 pr not.
Can anyone please help me with this? 'm new to memory level C prog.
|
BEGIN new.c output
buf[0] is 0x16
buf[1] is 0x254
END new.c output
Feel free to ask any questions about new.c:
/* BEGIN new.c */
#include <stdio.h>
#include <string.h>
int main(void)
{
unsigned short type = 0xFE10;
unsigned char buf[sizeof type] = {0};
unsigned byte;
/*
** copying 2 bytes of type which is 0xFE10 to buf
*/
memcpy(buf, &type, sizeof type != 1 ? 2 : 1);
puts("BEGIN new.c output\n");
for (byte = 0; byte != sizeof type; ++byte) {
printf("buf[%u] is 0x%u\n", byte, buf[byte]);
}
puts("\nEND new.c output");
return 0;
}
/* END new.c */
--
pete |
| |
| | | pete | |
| | Posted: Sat Sep 06, 2008 5:28 am Post subject: Re: reading byte by byte from memory | |
| | | |
pete wrote:
| Quote: | Ashit Vora wrote:
Hi,
I had one small query.
I 'm coping data from an unsigned short to a char*.
code is
#include<stdio.h
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
memset(buf,0,512);
//copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
}
here, how to I cehck if the data has been successfully copied or not.
the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
At server I wanna check if the value received is 0xFE10 pr not.
Can anyone please help me with this? 'm new to memory level C prog.
BEGIN new.c output
buf[0] is 0x16
buf[1] is 0x254
END new.c output
|
That's not really what I wanted.
I'll try again:
BEGIN new.c output
buf[0] is 0x10
buf[1] is 0xfe
END new.c output
/* BEGIN new.c */
#include <stdio.h>
#include <string.h>
int main(void)
{
unsigned short type = 0xfe10;
unsigned char buf[sizeof type] = {0};
unsigned byte;
/*
** copying all bytes of type which is 0xfe10 to buf
*/
memcpy(buf, &type, sizeof type);
puts("BEGIN new.c output\n");
for (byte = 0; byte != sizeof type; ++byte) {
printf("buf[%u] is 0x%x\n", byte, buf[byte]);
}
puts("\nEND new.c output");
return 0;
}
/* END new.c */
--
pete |
| |
| | | Bartc | |
| | Posted: Sat Sep 06, 2008 7:43 am Post subject: Re: reading byte by byte from memory | |
| | | |
Ashit Vora wrote:
| Quote: | #include<stdio.h
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
memset(buf,0,512);
//copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
}
here, how to I cehck if the data has been successfully copied or not.
the actual purpose is....... this is a client prog and I wanna send
the value of buf at the server.
At server I wanna check if the value received is 0xFE10 pr not.
Client's piece of code.
//total_buf_size is the sum of header plus data
total_buf_size=10;
buf =(char*) malloc (total_buf_size);
if(buf==NULL){
printf("Malloc Failed\n");
}
|
If buf_size is really only 10 bytes, you could just use char buf[10];
| Quote: |
memset(buf,0, total_buf_size);
memcpy(buf,&type,2);
memcpy(&buf[2],&offset,4);
memcpy(&buf[6],&data_length,4);
|
You seem to be filling a struct with values of 2,4 and 4 bytes. You might be
better off defining:
struct {
unsigned short sig;
int offset, data_length;
} header = {0xFE10, 0, 0};
BUT only if you can persuade your compiler not to leave a 2-byte gap between
..sig and .offset.
Then instead of memcpy:
header.offset=offset;
header.data_length=data_length;
| Quote: | /*now sending the data BYTE AT A TIME*/
for(i=0;i<10;i++){
if(send(client_sock,&buf[i],1,0)==-1){
perror("send");
exit(1);
|
Accessing buf (now header) a byte at a time is a little more tricky:
for (i=0; i<sizeof(header); ++i){
if send(client_sock, ((char*)&header+i),1,0)...
(Why can't you send all bytes at once? If you can do that, you can also send
0xFE10 as a 2-byte block, and offset and data_length as two 4-byte blocks,
you don't need the struct or buf)
Do something similar in the server code and check whether .sig or .sig is
0xFE10
--
Bartc |
| |
| | | Nick Keighley | |
| | Posted: Sat Sep 06, 2008 11:44 am Post subject: Re: reading byte by byte from memory | |
| | | |
On Sep 6, 5:55 am, Ashit Vora <a.k.v...@gmail.com> wrote:
| Quote: | I had one small query.
I 'm coping data from an unsigned short to a char*.
code is
#include<stdio.h
int main(void){
unsigned short type=0xFE10;
char * buf = char(*) malloc(512);
|
the cast is syntactically wrong and unnecessary
| Quote: | memset(buf,0,512);
//copying 2 bytes of type which is 0xFE10 to buf
memcpy(buf,type,2);
}
here, how to I cehck if the data has been successfully copied or not.
|
why wouldn't it be? use printf(), or memcmp() or a debugger
| Quote: | the actual purpose is.......
|
....... isn't standard punctuation
| Quote: | this is a client prog and I wanna send
the value of buf at the server.
|
"to the server"? For socket stuff try comp.unix.programmer (I think).
| Quote: | At server I wanna check if the value received is 0xFE10 pr not.
|
memcmp()?
| Quote: | Can anyone please help me with this? 'm new to memory level C prog.
|
I'm not sure what "memory level programming" is
--
Nick Keighley |
| |
|
|
