I'm currently busy with a project in which I have to copy a part from a file to another file, so I made a code for that using fread and fwrite. But I came across a problem: for testing purposes I made a code which should copy a whole file, but somehow the code creates copies that are larger than the original file. See the code I made below
FILE *base_file;
FILE *new_file;
fpos_t curpos;
int tmp;
// Open the base file
fopen_s(&base_file, "C:/base.dat", "rb");
// Open the file which should contain the copy
fopen_s(&new_file, "C:/new.dat", "w");
// Get the filesize
fseek(base_file, 0, SEEK_END);
fgetpos(base_file, &curpos);
fseek(base_file, 0, SEEK_SET);
//Read and copy (it seems to go wrong here)
for(int i = 0; i < curpos; i++){
fread (&tmp, 1, 1, base_file);
fwrite(&tmp, 1, 1, new_file);
}
fclose(base_file);
fclose(new_file);
The base file is 525 kb, and the newfile is 527kb. As far as I could see the parts where this problem occurs is after parts where there are 7 nullbytes, and the copy somehow has added a '0D'(in Hex) after these parts. In ascii the '0D' character is a 'carriage return'. I was wondering what could be the reason that my copy code adds carriage returns into the file? As far as I know this script should just work as I just read the basefile, and directly copy it to the newfile, and the basefile doesn't contain these carriage returns.
You're opening the destination file in text mode, instead of binary mode, so the newline translation happens behind your back. Change the mode to "wb".
Other notes:
Use streams rather than stdio.
Don't write byte-for-byte. Use a larger buffer, your method will take forever for larger files.
Will "wb" instead of "w" fix it?
Related
I can take the text file string with "fgets" and print it out one line using "SetWindowTextA". Like This code
FILE *p_file = fopen("Test.txt", "r");
if (p_file != NULL) {
text = fgets(temp, sizeof(temp), p_file);
m_Edit_load.SetWindowTextA(text);
fclose(p_file)
}
But I want to print out all the lines. I've used the code at the bottom, but only the last line printed
FILE *p_file = fopen("Test.txt", "r");
if (p_file != NULL) {
while(NULL != fgets(temp, sizeof(temp), p_file){
m_Edit_load.SetWindowTextA(temp);
}
fclose(p_file);
}
How can I print out all the rows?
Problem here is, SetWindowTextA is setting text, not appending. Hence, your window might be ending up with last line. To remove this problem, first create a dynamic array, append all characters, then call SetWindowTextA at last.
The most straightforward way is to open the file in binary mode, load it into a buffer and put it in the control through a single SetWindowText() call.
Depending on the format of the text file, it may require some additional steps:
If the file is ASCII, and of the same codepage as the system it runs on, a SetWindowTextA() call is OK.
If the file is Unicode it can be loaded onto the control by calling SetWindowTextW() - the control must be Unicode as well.
If the file is UTF-8 or ASCII, but in a codepage other than that of the system, the text must be converted to Unicode using the MultiByteToWideChar() function, before loaded onto the control.
Another conversion that may be needed is LF to CR-LF, if the lines are joined in the control. You need to write some code for this.
As already stated in one of the other answers, the problem is that SetWindowText will overwrite the text. Your code seems to incorrectly assume that this function will append the text instead.
If you want to set the edit control to the entire text of a file, then you will have to read the entire text of the file into a memory buffer, and pass a pointer to that memory buffer to SetWindowText.
The function fgets is used for reading a single line. Although you can solve your problem with fgets, there is no reason to limit yourself to only reading one line at a time. It would therefore be more efficient to read as much data as possible in one function call, for example by using the function fread instead of fgets.
Another issue is that you are opening your text file in text mode, which means that the \r\n line endings will get translated to \n. However, this is not what you want, because when using SetWindowText on a multiline edit control, the line endings must be \r\n, not \n. Therefore, you should change the line
FILE *p_file = fopen("Test.txt", "r");
to
FILE *p_file = fopen("Test.txt", "rb");
in order to open the file in binary mode.
The whole code should look like this:
FILE *fp = fopen( "Test.txt", "rb" );
if ( fp != NULL )
{
char buffer[4096];
size_t bytes_read;
bytes_read = fread( buffer, 1, (sizeof buffer) - 1, fp );
buffer[bytes_read] = '\0';
m_Edit_load.SetWindowTextA( buffer );
fclose(p_file);
}
If it is possible that 4096 bytes is not sufficient to contain the entire file, then you could increase the size of the buffer. However, you should not increase it too much, because otherwise, there is a danger of a stack overflow. Instead of allocating the memory buffer on the stack, you could also allocate it on the heap, by using malloc instead. Another alternative would be to use a static buffer, which also does not get allocated on the stack.
Using mingw under windows the following code which works under linux does not work:
int fh = open(filename, O_RDONLY);
const int size=100000;
int bytesRead = read(fh, buffer, size);
The file is bigger than 100k yet bytes read is just 232. I think this has something to do with binary files in windows?
This code with ifstream will work in windows and Linux.
ifstream in(filename, ios::binary);
const int size=100000;
in.read(buffer, size);
Is there a way to make level 2 IO calls work on windows as well?
Reading manuals is very useful technics.
_read
Return Value
_read returns the number of bytes read, which might be less than buffer_size if there are fewer than buffer_size bytes left in the file, or if the file was opened in text mode. In text mode, each carriage return-line feed pair \r\n is replaced with a single line feed character \n. Only the single line feed character is counted in the return value. The replacement does not affect the file pointer.
Text and Binary Mode File I/O
File I/O operations take place in one of two translation modes, text or binary, depending on the mode in which the file is opened. Data files are usually processed in text mode.
Use the function _set_fmode to change the default mode for newly opened files. Use _get_fmode to find the current default mode. The initial default setting is text mode (_O_TEXT).
Change the default translation mode directly by setting the global variable _fmode in your program. The function _set_fmode sets the value of this variable, but it can also be set directly.
open(filename, O_RDONLY); opens files in text mode in Windows by default.
open(filename, O_RDONLY | O_BINARY); opens files in binary mode in Windows and further read will read all requested bytes if there's enough bytes left in the file.
I'm trying to read from a file at a specific offset (simplified version):
typedef unsigned char u8;
FILE *data_fp = fopen("C:\\some_file.dat", "r");
fseek(data_fp, 0x004d0a68, SEEK_SET); // move filepointer to offset
u8 *data = new u8[0x3F0];
fread(data, 0x3F0, 1, data_fp);
delete[] data;
fclose(data_fp);
The problem becomes, that data will not contain 1008 bytes, but 529 (seems random). When it reaches 529 bytes, calls to feof(data_fp) will start returning true.
I've also tried to read in smaller chunks (8 bytes at a time) but it just looks like it's hitting EOF when it's not there yet.
A simple look in a hex editor shows there are plenty of bytes left.
Opening a file in text mode, like you're doing, makes the library translate some of the file contents to other stuff, potentially triggering a unwarranted EOF or bad offset calculations.
Open the file in binary mode by passing the "b" option to the fopen call
fopen(filename, "rb");
Is the file being written to in parallel by some other application? Perhaps there's a race condition, so that the file ends at wherever the read stops, when the read is running, but later when you inspect it the rest has been written. That would explain the randomness, too.
Maybe it's a difference between textual and binary file. If you're on Windows, newlines are CRLF, which is two characters in file, but converted to only one when read. Try using fopen(..., "rb")
I can't see your link from work, but if your computer claims no more bytes exist, I'd tend to believe it. Why don't you print the size of the file rather than doing things by hand in a hex editor?
Also, you'd be better off using level 2 I/O the f-calls are ancient C ugliness, and you're using C++ since you have new.
int fh =open(filename, O_RDONLY);
struct stat s;
fstat(fh, s);
cout << "size=" << hex << s.st_size << "\n";
Now do your seeking and reading using level 2 I/O calls, which are faster anyway, and let's see what the size of the file really is.
When I do
fstream someFile("something.dat", ios::binary|ios::out);
someFile.seekp(someLocation, ios::beg);
someFile.write(someData, 100);
It seems to replace the entire file with those 100 bytes instead of replacing only the appropriate 100 bytes, as if I had specified ios::trunc. Is there a portable way to not have it truncate the file?
Edit: adding ios::in seems to do the trick, by why is this required, and is that standard behavior?
Edit #2: I am not trying to append to the existing file. I need to replace the 100 bytes while leaving the rest unaffected.
You want the append flag, ios::app, if you want to write at the end of the file.
To do it somewhere arbitrarily in the middle of the file, you need to seek to the right place. You CAN do this by opening the file for in and out, but if I were you I'd create a temp file, copy input up to mark, write your new data, copy the rest to EOF, close the files and replace the previous version with the temp file. This is called a "Master File update".
AFAIR ios::out only specifies the file is for output and ios:binary only specifies the files is binary. The default behaviour for a stream is to create a new file and overwrite the old file. If you want to modify an existing file you must open the file with the ios::app flag.
ATM I cannot check my references so be sure to double check, but I felieve that is accurate.
Since the file already exists open it in 'read+write' mode and then do seekp. I think it will work.
fstream someFile("something.dat", ios::binary|ios::out|ios::in);
someFile.seekp(someLocation, ios::beg);
someFile.write(someData, 100);
The ios:in mask tells the file pointer to position at the beginning of the file so it can start reading in from the start. But, you may want to use fseek to set the file pointer at the beginning of the file.
What translation occurs when writing to a file that was opened in text mode that does not occur in binary mode? Specifically in MS Visual C.
unsigned char buffer[256];
for (int i = 0; i < 256; i++) buffer[i]=i;
int size = 1;
int count = 256;
Binary mode:
FILE *fp_binary = fopen(filename, "wb");
fwrite(buffer, size, count, fp_binary);
Versus text mode:
FILE *fp_text = fopen(filename, "wt");
fwrite(buffer, size, count, fp_text);
I believe that most platforms will ignore the "t" option or the "text-mode" option when dealing with streams. On windows, however, this is not the case. If you take a look at the description of the fopen() function at: MSDN, you will see that specifying the "t" option will have the following effect:
line feeds ('\n') will be translated to '\r\n" sequences on output
carriage return/line feed sequences will be translated to line feeds on input.
If the file is opened in append mode, the end of the file will be examined for a ctrl-z character (character 26) and that character removed, if possible. It will also interpret the presence of that character as being the end of file. This is an unfortunate holdover from the days of CPM (something about the sins of the parents being visited upon their children up to the 3rd or 4th generation). Contrary to previously stated opinion, the ctrl-z character will not be appended.
In text mode, a newline "\n" may be converted to a carriage return + newline "\r\n"
Usually you'll want to open in binary mode. Trying to read any binary data in text mode won't work, it will be corrupted. You can read text ok in binary mode though - it just won't do automatic translations of "\n" to "\r\n".
See fopen
Additionally, when you fopen a file with "rt" the input is terminated on a Crtl-Z character.
Another difference is when using fseek
If the stream is open in binary mode, the new position is exactly offset bytes measured from the beginning of the file if origin is SEEK_SET, from the current file position if origin is SEEK_CUR, and from the end of the file if origin is SEEK_END. Some binary streams may not support the SEEK_END.
If the stream is open in text mode, the only supported values for offset are zero (which works with any origin) and a value returned by an earlier call to std::ftell on a stream associated with the same file (which only works with origin of SEEK_SET.
Even though this question was already answered and clearly explained, I think it would be interesting to show the main issue (translation between \n and \r\n) with a simple code example. Note that I'm not addressing the issue of the Crtl-Z character at the end of the file.
#include <stdio.h>
#include <string.h>
int main() {
FILE *f;
char string[] = "A\nB";
int len;
len = strlen(string);
printf("As you'd expect string has %d characters... ", len); /* prints 3*/
f = fopen("test.txt", "w"); /* Text mode */
fwrite(string, 1, len, f); /* On windows "A\r\nB" is writen */
printf ("but %ld bytes were writen to file", ftell(f)); /* prints 4 on Windows, 3 on Linux*/
fclose(f);
return 0;
}
If you execute the program on Windows, you will see the following message printed:
As you'd expect string has 3 characters... but 4 bytes were writen to file
Of course you can also open the file with a text editor like Notepad++ and see yourself the characters:
The inverse conversion is performed on Windows when reading the file in text mode.
We had an interesting problem with opening files in text mode where the files had a mixture of line ending characters:
1\n\r
2\n\r
3\n
4\n\r
5\n\r
Our requirement is that we can store our current position in the file (we used fgetpos), close the file and then later to reopen the file and seek to that position (we used fsetpos).
However, where a file has mixtures of line endings then this process failed to seek to the actual same position. In our case (our tool parses C++), we were re-reading parts of the file we'd already seen.
Go with binary - then you can control exactly what is read and written from the file.
In 'w' mode, the file is opened in write mode and the basic coding is 'utf-8'
in 'wb' mode, the file is opened in write -binary mode and it is resposible for writing other special characters and the encoding may be 'utf-16le' or others