11
votes
Accepted
If I use fread in a while loop, will it move the file pointer?
When you do an fread, whether it is in a while loop statement or anywhere else, it will execute the read and will most definitely move the file pointer. The pointer will be repositioned to the first ...
- 68.4k
4
votes
Accepted
Recover pset 4 last image
It's a fairly common error with this pset. The last file is one 512 byte block too long. The logic structure of this program is:
Read a block of data
process the block of data
check for EOF
When ...
- 68.4k
4
votes
Accepted
PSet4 Recover, only finds 22 corrupted photos, doesn't pass Check50
This is a pretty common newbie mistake. Look at this code:
//Loop until end of 512 block
while (fread(buffer, sizeof(BYTE), 512, memorycard) == 512)
{
//Read 512 bytes into buffer
fread(buffer, ...
- 68.4k
3
votes
PSET4, Recover - Generated JPGs are blank
I think you complicate your program unnecessarily with calls to functions that do not clarify the code, recover can be done in a simpler way, and personally I always look for the greatest possible ...
- 5,169
3
votes
Accepted
PSET4, Recover - Generated JPGs are blank
Mars is right, the code is too complex. Too much complexity around opening, closing, and testing for open files. It's understandable that when code is executed repeatedly, you'd want to create a ...
- 68.4k
3
votes
Accepted
Why does the 0.49 jpg file doesn't match correctly?
This is a very common problem. ;-)
Think carefully about how the while loop ends. It checks to see if the EOF flag is set. If it isn't, it loops again. The problem is that the EOF flag isn't set ...
- 68.4k
2
votes
Accepted
PSET4 Recover Can't Open JPEGs in the IDE
Can you give me an example of a filename that is supposed to contain a line feed?
sprintf(outfile, "%03i.jpg\n", foundPhoto);
As a side note, a programming tip. When you see to nearly ...
- 68.4k
2
votes
Accepted
recover pset4 file handling
1 It's not a single char. You've declared an array of 8 chars, which is what you need to hold "000.jpg"
{'0', '0', '0', '.', 'j', 'p', 'g', '\0'}
2 bookmark is an array. An array will "decay" to a ...
- 18.6k
2
votes
Accepted
PSet4 recover: recovered files start with a wrong sequence
The whole problem is given by the following statement:
char fileName[7];
The file name is given by seven characters, but you must bear in mind that it is a string, so we need an additional character ...
- 5,169
2
votes
Accepted
pset4 recover.c Why are my pictures scrambled?
De Morgan's laws
The opposite of
buffer[0] == 0xff &&
buffer[1] == 0xd8 &&
buffer[2] == 0xff &&
(buffer[3] & 0xf0) == 0xe0
is
buffer[0] != 0xff ||
...
- 20.9k
2
votes
Can't open generated JPGs
In fwrite(inPointer, 1, number, newFilePointer);, inPointer should be buffer, you don't want to write the content of the FILE structure to disk, but the bytes you read.
Interesting part is - your ...
- 20.9k
2
votes
Accepted
PSET4 Recover spits out 50 images but they're all invalid
Effectively your algorithm is correct, but there is a small mess with the pointers, you declare a pointer to the buffer in which it will be written:
uint8_t *buffer_ptr = malloc(FAT_BLOCK_SIZE);
So, ...
- 5,169
2
votes
Accepted
pset4 recover 049.jpg recovered image does not match
Your last file has one extra block of data. Look at this code:
//do untill end of file
while (!(feof(rawCard)))
{
//read 512 bytes and look for JPEG in first 4 bytes
fread(bytes, 512, 1, ...
- 68.4k
2
votes
Accepted
Pset 4 - Fopen returns NULL
This "argv[1]" is the string literal argv[1] (because of the "s), and no such file name exists.
- 28k
2
votes
Accepted
(pset4) Fatal error: glibc detected an invalid stdio handle
At line 46, you write to the outside of filename declared at line 27. Here is the link that you can debug errors like this by yourself.
Memory access error: writing to the outside of a memory ...
- 450
2
votes
Accepted
Understanding the contents of the raw file
It looks like gibberish because the code is printing it as if it were ASCII char data. In reality, it is literally raw digital data. It doesn't translate to ASCII codes or anything else. Instead, it ...
- 68.4k
2
votes
Accepted
Pset4 Recovery Produces Corrupt Null Files & Skips An Image
"Ready, fire, aim!"
The problem lies here:
jpg = fopen(filename, "w");
sprintf(filename, "%03i.jpg", numfound);
The sprintf command builds the name of ...
- 68.4k
2
votes
Accepted
PSET4 Recover: Check50 shows error
It's a problem with processing the EOF condition on the input file. The code is structured so that it reads in 512 bytes, copies them out to the output file, and then checks for EOF. In other words, &...
- 68.4k
2
votes
CS50 Recover recovering corrupted images, and only 43 images
There are several issues in this code.
First, look at how i is being incremented. Inside the code, it is incremented by 512 in several places, but it's also being incremented by 1 in the for loop ...
- 68.4k
2
votes
Accepted
Code for Good ol' Recover returns all fifty images (000-049), but doesn't pass Check50
actually, the code seems to be creating 52 files, numbered 000 to 051, so something is amiss.
Perhaps you should consider reworking the logic a little bit?
Hint: why open an output file before the ...
- 68.4k
2
votes
Accepted
in pset4, recover, why is the first jpg found treated differently from the other jpg files?
Half of the answer lies in the program spec. All the data in the file before the first signature is garbage data to be discarded.
The other half should be simple. Before using a file pointer to open ...
- 68.4k
2
votes
CHECK50 Passes, but I Get 6/7 When Submitting
check50 is timing out because your program takes longer to run than is allowed.
It comes down to this
Your buffer is unsigned char *buffer = malloc(512);
Your fread is fread(buffer, 1, sizeof(buffer), ...
- 18.6k
1
vote
PSet 4 Recover works, but returns 1, not 0. HELP!
bmp.h doesn't exist in check50 for this assignment, so the file is never included. This leads to compile errors.
You'll need to incorporate the definition of BYTE into recover.c, or use another ...
- 68.4k
1
vote
Accepted
pset4 recover - jpgs in place, 0 is returned, but Check50 fails - segfault
The problem is due to a data overwrite bug. The problem lies in these two lines:
char jpgName[4]; // array for 3 symbols with trailing 0
....
// give a name and write the 1st block
...
- 68.4k
1
vote
Accepted
PSET 4 - RECOVER
You write first sector twice for each file. Remove first fwrite(buffer, 512, 1, img);
And I'd put another if (img != NULL) in front of the second fclose(img); in case the dump contains no JPEG file ...
- 20.9k
1
vote
Accepted
pset4 recover single image
A loop is definitely the way to go, not if statements.
Now, have you looked at the size of the file(s) produced? I suspect that the first file created is much larger than it should be - a ...
- 68.4k
1
vote
Accepted
Problem Set 4 Recover Issues. I can't figure out why my code doesn't work
You have multiple fread, each reading 512 bytes, but not every read sector seems to be written even after opening a file. This means you're skipping some sectors.
Instead of a do..while loop, use a ...
- 20.9k
1
vote
Accepted
How to solve the segmentation fault in pset4 recover?
Since it should persist over multiple iterations, move FILE* photo = NULL; above your loop. Otherwise you're creating a new variable each iteration and set it to NULL, which makes fwrite fail.
Second ...
- 20.9k
1
vote
Pset4 recover- cannot open file for writing error
Also, newfile needs to contain the name of the file to be opened. It never has the filename assigned to it.
- 68.4k
1
vote
Accepted
Pset4 recover- cannot open file for writing error
int p=0;
char *newfile = malloc(sizeof(buffer)*p);
You actually have zero bytes reserved with malloc
- 5,169
Only top scored, non community-wiki answers of a minimum length are eligible