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There have been many rookie errors pointed out by others, so I won't repeat them. There are a few general things that will help with your code:
1. Compile the code with the strictest warnings setting. The compiler will likely tell you about a lot of bugs, or potential bugs, lurking in the code. Do not use the code until there are no warnings.
2. Use a static code analyzer like Lint. It would have caught problems like your assign/compare bug. It will also offer many suggestions for cleaner code.
See http://en.wikipedia.org/wiki/List_of_tools_for_static_code_analysis[^]
When you can compile code with no warnings, and get through Lint without much trouble, you are much less likely to have a real problem with your code. You'll be able to concentrate on the real meat of the code.
Stuart
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Silly question -- in whatever language your working in, is there no find command?
If not, write one....you're doing the same action 3+ times. Take an value and an array and search through the array looking for the element. Return -1 if not found or the index value if it is found.
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This code is not C. It could be C++ or Java. A string in C IS a character ARRAY and is not declared as string but as char[string length+1].
Try:
if (arg1.equal(a))
{
tp = counter;
}
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Content of a.txt
Hello How are you
Welcome
Function used to read the File
void ReadBytes(__inout BYTE *pBuffer, DWORD dwSize)
{
DWORD dwRead;
if (hFile != INVALID_HANDLE_VALUE)
ReadFile(hFile,pBuffer,dwSize,&dwRead,NULL);
}
int main()
{
myFile mObj;
BYTE* hSrc = new BYTE[26];
mObj.ReadBytes(hSrc,26);
std::cout<<hSrc;
return 0;
}
The output of the above function gives.
Hello How are you
Welcomeýýýý««««««««îþ
Why this extra characters at the end? please help
Some Day I Will Prove MySelf :: GOLD
modified on Tuesday, February 1, 2011 12:44 AM
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goldenrose9 wrote: Why this extra characters at the end?
Because cout will output characters until it reaches a \0.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
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i had checked this with file mapping. In file mapping when i use cout to display the hSrc value it gives the correct output.
then why it is displaying extra characters when i am using ReadFile method. Is there any problem in my code. please help
Some Day I Will Prove MySelf :: GOLD
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goldenrose9 wrote: ...then why it is displaying extra characters when i am using ReadFile method.
It has nothing to do with ReadFile().
goldenrose9 wrote: Is there any problem in my code.
Yes, hSrc is not terminated properly.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
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then how to solve this.
Some Day I Will Prove MySelf :: GOLD
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See here.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
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You forgot to terminate the buffer with the null-termination character:
int main()
{
myFile mObj;
BYTE* hSrc = new BYTE[27];
mObj.ReadBytes(hSrc,26);
hSrc[26] = '\0';
std::cout<<hSrc;
return 0;
}
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thanx  
Some Day I Will Prove MySelf :: GOLD
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Cedric Moonen wrote: BYTE* hSrc = new BYTE[27];
here you have initialized the byte array with +1 of the required value that is 26 and null terminated the byte array at 26.
A small doubt. do i have to allocated the byte array +1
Some Day I Will Prove MySelf :: GOLD
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Yes, you have to take the termination character into account (it still counts as one char and should be allocated too). Remember that if I allocate an array of 27 characters, the last one is the character at index 26 (since the array is zero-based).
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got it.
sir, now the program is working fine. but when i pass a bmp or exe file to this function only few bytes from the starting is read into the buffer.
Zip Archive
PK
EXE
MZ
BMP File
BM:
am i missing something again.please help..
Some Day I Will Prove MySelf :: GOLD
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Are you trying to print those files to the console ? 
This won't work, since they contain binary information which can perfectly be the character with ASCII code 0 (which will be considered as the end of the string). What are you trying to do here ?
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Hi,
Using C++, std::fstream, Windows.
I have an algorithm that processes large file (actually this is the series of algorithms, but lets consider only one, cause others having the same problems).
In general this algorithm reads chunks of data from one file and write to the other file with during some realignment (For reference, I'm doing realignment of the 3d volume data). I'm reading chunk size is 512 bytes, writing chunk size is 16 kb.
Usually this algorithm finishes in 1 minute and 50 seconds. But I noticed that sometimes (rarely) it finishes in 24 seconds! Processing the same file, the same execution path. I've started to search for the reasons of why this slowdown is happening and how can I control that.
1) I have tried increasing the coalescing of the accesses to disk
2) I have considered the fragmentation problem (the file that I write is wrote in small chunks, therefore it's fragmented, about 600 fragments). When I resolved fragmentation problem (so, it's guaranteed that file is not fragmented) - I didnt got anything, still this chaotic access speed.
3) I have investigated the probability, that Windows flashes my memory buffers to HDD. No, that's not the case.
4) I have found that if I do all this operation on the other physical disk (not the one with OS) - I get this slow down more rarely, and algorithm usually finishes in 40 seconds (but anyway, speed is of HDD access is chaotic).
Frequently during the same execution, access speed is rising or falling down, may be few times.
This looks like my accesses are going out of tact with some internal HDD or OS operations, don't know.
Anyone, have some experience or idea?
Thanks.
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If you read and write data from the same disk from different files, the read-head will have to move to a different place on the disk, which is slow. If your input and output file are on different drives, this problem is solved. If you read and write alternatively (to the same physical disk) in your program each time, this slow down is maximum.
Note that some variation in disk speed can't be prevented in a multitasking OS where other programs might be using the disk too.
If your memory permits, you could consider reading the entire input file to memory at once at the beginning of your algorithm and then processing it and writing the results.
modified 13-Sep-18 21:01pm.
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My files are always one the same drive in all tests. When it does in 1:54 or 24 seconds.
Thaddeus Jones wrote: Note that some variation in disk speed can't be prevented in a multitasking OS where other programs might be using the disk too.
I always ensure no other work is running. Also I'm looking in the "Resource monitor", no big HDD accesses except my program.
Thaddeus Jones wrote: If your memory permits, you could consider reading the entire input file to memory at once at the beginning of your algorithm and then processing it and writing the results.
No this is not possible, algorithm should work with unlimited file size.
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Maybe you could increase your input buffer then from 512 bytes to say 100Mb, and every time you've processed the 100Mb from memory, you'll read a new 100Mb. Similarly, writing your output to a memory buffer (say also 100Mb) and once your buffer is full writing that to file, should help with speed too.
The idea is to concentrate disk access to areas on the disk that are near eachother, since those access operations are much faster than if the head has to be repositioned.
modified 13-Sep-18 21:01pm.
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Thaddeus Jones wrote: Maybe you could increase your input buffer then from 512 bytes to say 100Mb, and every time you've processed the 100Mb from memory, you'll read a new 100Mb. Similarly, writing your output to a memory buffer (say also 100Mb) and once your buffer is full writing that to file, should help with speed too.
I've tried this approach. Although it gives slight speed increase, it doesnt resolve the problem of chaotic speed.
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I'm afraid I'm out of ideas then
modified 13-Sep-18 21:01pm.
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The problem is not "Algorithm is slow", but "Algorithm speed is too chaotic". Sometimes it's done 5 times faster then usual, this means - it should always be done 5 times faster.
I agree, that access speed can vary a little, but 5 times... I think this is something that should be puzzled out.
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progDes wrote: Usually this algorithm finishes in 1 minute and 50 seconds. But I noticed that sometimes (rarely) it finishes in 24 seconds! Processing the same file, the same execution path. I've started to search for the reasons of why this slowdown is happening and how can I control that.
Caching, perhaps?
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
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There are countless factors that could be contributing to this.
I would guess that the major ones are file caching and delayed writes[^].
File Caching:
When a file is opened and read, its contents are loaded into RAM by the OS, and then sections are copied to your exe as you need them (usually in 4KB chunks which you then read smaller chunks from). Once the file is closed it is marked as unused but the OS, but is not removed from the RAM. If then another program needs heaps of memory the file will be removed from the RAM, however if this does not happen, and your file is still in the RAM then your program doesn't actually need to use the hard disk.
This is most notable if you open a program that uses lots of files on load, say MS Word. If you then close the program and open it again shortly after without opening something else the 2nd time you open the program it will load much quicker.
Delayed Writes:
These generally only occur to slow mediums such as USB memory sticks, however they can happen to HDD as well.
When you write to a file, and storage device is busy the data you write will often get written into a virtual file in RAM which is then written to the storage device at a later stage.
Other problems may include HDD head seeks (as mentioned by Thaddeus Jones) and other programs accessing the disk.
If you are running Windows vista or 7 then you can look at disk accesses with the Resource Monitor (resmon.exe)
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Thanks Adrew,
I will consider the situation with file caching. Need to investigate on this more.
Meanwhile, are you think that rare disk accesses by other programs can reduce speed of my accesses in 5 times?
I'm making sure that no heavy HDD operations are performed by other programs, but other programs for sure doing disk accesses even in the idle mode.
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