Questions tagged [seekg]
89 questions
26
votes
1 answer
fstream seekg(), seekp(), and write()
I'm looking for some clarification on how seekg() and seekp() works with respect to when you are writing to a file. Say for instance I had a file like so:
offset 0: 2
offset 4: 4
offset 8: 6
offset 12: 8
offset 16: 10
Now I want to open the file…
raphnguyen
- 3,565
- 18
- 56
- 74
25
votes
2 answers
What's wrong with the ifstream seekg
I am trying to do a seek and re-read the data. but the code fails.
The code is
std::ifstream ifs (filename.c_str(), std::ifstream::in | std::ifstream::binary);
std::streampos pos = ifs.tellg();
std::cout <<" Current pos: " << pos <<…
veda
- 6,416
- 15
- 58
- 78
16
votes
1 answer
How to check whether ifstream is end of file in C++
I need to read all blocks of one large file(about 10GB) sequentially, the file contains many floats with a few strings, like this(each item splited by '\n'):
6.292611
-1.078219E-266
-2.305673E+065
sod;eiwo
4.899747e-237
1.673940e+089
-4.515213
I…
user1024
- 982
- 4
- 13
- 26
13
votes
4 answers
How to read a growing text file in C++?
I am trying to read from a file which is growing (something similar to what tail -F does), but there must be some problems with my code:
string log, logFile("test.log");
size_t p = 0;
while(true)
{
ifstream ifs(logFile.c_str());
…
Pietro
- 12,086
- 26
- 100
- 193
10
votes
1 answer
Is using istream::seekg too much expensive?
In c++, how expensive is it to use the istream::seekg operation?
EDIT: How much can I get away with seeking around a file and reading bytes? What about frequency versus magnitude of offset?
I have a large file (4GB) that I am parsing, and I want to…
Brian
- 3,453
- 2
- 27
- 39
10
votes
3 answers
seekg cannot handle file of 4294967295 bytes properly
I found that in VS2010, seekg function does not work properly when file of exactly 4294967295 bytes is opened.
I'm using simple code:
#include
#include
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
…
Rusty
- 143
- 1
- 7
9
votes
1 answer
Why seekg does not work with getline?
Seekg does not seem to work, when I reach EOF in myFile.
ifstream myFile("/path/file");
for(int i; i < 10; i++){
myFile.seekg(0);//reset position in myFile
while(getline(myFile, line)){
doSomething
}
}
So, now I am opening…
rluks
- 2,762
- 8
- 38
- 56
8
votes
2 answers
fstream - How to seekg() to position x from end
I'm looking for a way to set my get pointer at position x from the end of an fstream.
I tried
file.seekg(-x, ios_base::end);
But according to this question, this line is undefined behavior.
How can I, in any way, seek to position x from the end of…
user2962533
- 397
- 1
- 5
- 18
7
votes
1 answer
How do I implement seekg() for a custom istream/streambuf?
I used to be a C++ expert a decade ago, but for the past 10 years I've been programming Java. I just started a C++ project that uses a small third-party XML parser. The XML parser accepts an STL istream. My XML data is coming from a Windows COM…
Garret Wilson
- 18,219
- 30
- 144
- 272
7
votes
3 answers
C++ Reading file backwards from the end of the file
I am trying to write a program with a menu that reads from a text file a few different ways. I'm just working on menu option #2 still (reading backwards from the end of the file), but I can't wrap my head around what I'm doing wrong. I've been at…
tp77
- 131
- 2
- 2
- 4
7
votes
1 answer
How does seekg find the end of the file?
In a scenario using seekg & tellg on a file, I was wondering what is happening under the hood?
// Open file and get file size
int myFileSize;
std::fstream myFile;
myFile.open(myFileName, std::ios::in|std::ios::binary);
if…
Lakey
- 1,948
- 2
- 17
- 28
5
votes
1 answer
C++ how to check if a stream (iostream) is seekable
Is there a way I can check if an istream of ostream is seekable?
I suspect doing a test seek and checking for failbit is not correct
since the seek can fail for unrelated reasons.
I need this to work on Linux and mac, if that makes a difference.
ATemp
- 319
- 3
- 10
4
votes
1 answer
why does a blank line occupy to two bytes?
I'm new to C++. I'd like to count the blank lines at the end of a text file. But now i meet a problem. The contents of the text file are like:
test.txt
1
2
blank line
The code is:
#include
#include
using namespace std;
int…
Oliver Yu
- 99
- 5
4
votes
3 answers
C++ slow read/seekg
In my program I read in a file (here only a test file of about 200k data points afterwards there will be millions.) Now what I do is:
for (int i=0;i
magu_
- 4,766
- 3
- 45
- 79
3
votes
0 answers
Extraction operator causing my program to exit?
I'm a usual lurker but this is my first post! I understand you guys like detail so I will do my best. I will appreciate whatever input anyone has.
I am working on an overloading the extraction operator for an object with a dynamic array of digits.…
spanishgum
- 1,030
- 1
- 14
- 29