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Two problems
- Thread starter Newaz
- Start date
"wb" means open a file for writing in binary mode. "rb" means open a file for reading in binary mode.
You'll see casts a lot in C, however they are actually not needed very often. You should think carefully about what you're doing and *why* you're using a cast, you'll often discover that you don't need a cast and that you were operating under a misconception.
Some reasonable uses of casts:
size_t foo=5;
printf("%lu\n",(unsigned long)foo);
Since there is no conversion specifier for size_t (the new standard changes this) you need a cast here to make printf happy.
int compare(const void *s1,const void *s2)
{
char *string1=(char *)s1;
char *string2=(char *)s2;
/* ... */
}
This could be a function to pass to the standard library function qsort(). Since qsort() doesn't know about the representation of the objects in the arrays it sorts, the parameters here must be "generic" pointers to void. The user, knowing about the objects in the array then needs to cast the void pointers the appropriate type before operating on them.
HTH,
Russ
bobbitts@hotmail.com
You'll see casts a lot in C, however they are actually not needed very often. You should think carefully about what you're doing and *why* you're using a cast, you'll often discover that you don't need a cast and that you were operating under a misconception.
Some reasonable uses of casts:
size_t foo=5;
printf("%lu\n",(unsigned long)foo);
Since there is no conversion specifier for size_t (the new standard changes this) you need a cast here to make printf happy.
int compare(const void *s1,const void *s2)
{
char *string1=(char *)s1;
char *string2=(char *)s2;
/* ... */
}
This could be a function to pass to the standard library function qsort(). Since qsort() doesn't know about the representation of the objects in the arrays it sorts, the parameters here must be "generic" pointers to void. The user, knowing about the objects in the array then needs to cast the void pointers the appropriate type before operating on them.
HTH,
Russ
bobbitts@hotmail.com
- Thread starter
- #3
Thanks for your answer rbobitts.
But I have some confusions
Such as
1)When we use "wb" and "w"? actually what is difference between that twos? Same question about "rb" and "r".
Please let me know.
Thanks
All the best.
Newaz
But I have some confusions
Such as
1)When we use "wb" and "w"? actually what is difference between that twos? Same question about "rb" and "r".
Please let me know.
Thanks
All the best.
Newaz
wb is write binary, which writes a stream of bits into the file, and w is just write, which is probably ASCII. Same with r and rb. For example, say that an ASCII A is represented by the binary string
011010101 (It's not, but bear with me)
using w, you would write an A in the file.
using wb, you would write 011010101 in the file.
Again, binary writes the literal binary information, and wirte writes teh higher level representation As always, I hope that helped!
Disclaimer:
Beware: Studies have shown that research causes cancer in lab rats.
011010101 (It's not, but bear with me)
using w, you would write an A in the file.
using wb, you would write 011010101 in the file.
Again, binary writes the literal binary information, and wirte writes teh higher level representation As always, I hope that helped!
Disclaimer:
Beware: Studies have shown that research causes cancer in lab rats.
Guest_imported
New member
- Jan 1, 1970
- 0
Just to add to what ever that has been put across.
When you write details in a file using the ASCII mode "w" instead of "wb", all non printable symboys (eg '\n') etc will take their action instead of just being written....
if the same operation were to be written in Binary mode "wb" the information is stored as-it-is without the action taking place.
Regards,
Shiv
PS: Correct me if I am wrong. To err is human
When you write details in a file using the ASCII mode "w" instead of "wb", all non printable symboys (eg '\n') etc will take their action instead of just being written....
if the same operation were to be written in Binary mode "wb" the information is stored as-it-is without the action taking place.
Regards,
Shiv
PS: Correct me if I am wrong. To err is human
well!i know about "wb" and 'w'.
wb=in this mode file will be open in binary format and in write mod.
in accessing binary files,the compiler performs no traslation of the newline(or any other)characters at all.Bytes are stored or retrieved as they appear in the stream.thus binary format is useful where files have no line structure(e.g.,executable files), or where each byte must be preserved the way it is,without compiler-determined interpretations.there are other options:"rb","ab","ab+" etc.
wb=in this mode file will be open in binary format and in write mod.
in accessing binary files,the compiler performs no traslation of the newline(or any other)characters at all.Bytes are stored or retrieved as they appear in the stream.thus binary format is useful where files have no line structure(e.g.,executable files), or where each byte must be preserved the way it is,without compiler-determined interpretations.there are other options:"rb","ab","ab+" etc.
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