Read large file in C++

Question

I manage a PDF file whose size is 2.15GB, I opened the file with fopen, I use _fseeki64 and _ftelli64 in order to get or update the pointer position in the file and it works correctly.

I use fread in order to read from the pdf file. Usually it works properly, but when the read pointer is located near to the end of the file, fread get the EOF character which is wrong.

So, how can I read correctly from this large PDF file.

NB: I use the same source code with file whose size is less than 2GB and it works correctly.

Can you reduce the code to a short program that reliably demonstrates the problem? Until you do, no one can help, since there is no knowing what you do wrong. — StoryTeller - Unslander Monica, Jun 02 '16 at 09:56
" when the read pointer is located near to the end of the file, fread get the EOF character which is wrong" - can you elaborate on that? — Rishit Sanmukhani, Jun 02 '16 at 09:56
Can you guarantee that the process is not running out of available memory while reading in the file? — stefaanv, Jun 02 '16 at 10:20
What platform are you using? What large file compiler options of #define's are you using? — David Schwartz, Jun 03 '16 at 06:32
`fread` receives `size_t`, so if `size_t` is 32 bits then it probably won't work with large files — phuclv, Jun 03 '16 at 07:10
@LưuVĩnhPhúc: size_t won't be an issue while working with file of size 2.15GB on 32 bit system. — sameerkn, Jun 03 '16 at 07:24
@sameerkn some personal code may use that as a signed type without noticing — phuclv, Jun 03 '16 at 08:24
Your question would do well to include some example code that exhibits the problem and to specify the compiler used and target OS. Everything that would enable a third-party to reproduce the problem in fact. — Clifford, Jun 03 '16 at 08:35
@sameerkn and it happens even in proper code but buggy compiler/stdlib, like you can see [here](http://stackoverflow.com/a/16325024/995714) — phuclv, Jun 04 '16 at 03:36

score 2 · Answer 1 · answered Jun 02 '16 at 10:33

2

Sounds to me that your're seeing the 2G limit of a signed 32-bit integer. The maximum value of such a variable is 2,147,483,647.

Edit

Use a debugger and check the actual value and type sent to _fseeki64and _ftelli64.

answered Jun 02 '16 at 10:33

anorm

2,255
1
19
38

score 0 · Answer 2 · edited May 23 '17 at 12:31

0

With a modern compiler (VS2012+ on Windows) you can use fstream which is the standard way to access large files.

See this answer for details.

edited May 23 '17 at 12:31

Community

1
1

answered Jun 03 '16 at 07:01

graham.reeds

16,230
17
74
137

score 0 · Answer 3 · edited May 23 '17 at 11:52

0

Since you mentioned things like EOF, so please check if you are using fread properly. Most importantly the loop if its there in which you try to read data in chunks.

Please check if you are not a victim of Wrongly using loop while using fread

edited May 23 '17 at 11:52

Community

1
1

answered Jun 03 '16 at 07:28

sameerkn

2,209
1
12
13

score 0 · Answer 4 · answered Jun 03 '16 at 08:20

0

There is no matter with the fread function, But, the read pointer of the file was already located at the end of the file. That's why it return EOF. When I change the read pointer position, fread works properly.

answered Jun 03 '16 at 08:20

ZINEBA

33
1
6

1

This information should be added to your question by editing it not posted as an *answer* - SO is not a discussion forum. – Clifford Jun 03 '16 at 08:31

Read large file in C++

4 Answers4