This is my first contact with C++.I have to make program that will monitor one .txt or .doc file and read every new(last) entry(word) from it.Only thing that I was able to do by now is to completely read txt file, but that is not the point, I can't even get only last word from txt file so I would really appreciate your help with this.
Thank you all in advance!!!
Not sure if this is homework, and just in case it is I'm trying to avoid spoiling it by "telling to much", and instead point you to the key ideas you could use.
To avoid reading the whole file, you could use first use the seekg method to position the file a certain number of bytes from the end, then perform the "read to the last word" from there.
To perform the "read to the last word" task proper (net of the optimization of not reading the whole file one word at a time, for which see first paragraph) use the >> operator with the std::ifstream as the left operand and a std::string as the right operand: just put this in a while(!thestream.eof()) { ... } so it will keep reading until it has the last word.
BTW, note that reading the text from a .doc file will be orders of magnitude harder than reading it from a text file, unless you can use a suitable ".doc-reading library" (the standard C++ library has no such functionality, per se).
Reading from MS Word from C++ is a tedious task; you'll need to get through the jumble of COM interfaces. Since you are saying it's your first contact with C++, my advice is to concentrate on plain text instead, namely on getting the last line of a plain text file.
I would do something like this. Provide your implementations of ReadFromEnd and FindRightmostLineSeparator, they should be trivial, and initialize the fileSize variable.
int const INITIAL_BUFFER_SIZE = 64;
int bufferSize = INITIAL_BUFFER_SIZE;
char* lastLine = NULL;
std::auto_ptr<char> buffer (new char[buffer_size]);
while(true) {
ReadFromEnd(buffer, buffer_size);
lastLine = FindRightmostLineSeparator(buffer);
if (lastLine == NULL && bufferSize == fileSize)
lastLine = buffer;
if (lastLine)
break;
buffer_size *= 2;
if (buffer_size > fileSize)
bufferSize = fileSize;
buffer.reset(new char[buffer_size]);
}
// lastLine contains the pointer to your last line
Related
Using C++ MFC with Visual Studio 2008, I am trying to using CFile or CStdioFile to read in the last line of a text document, store it, and then reprint it after the file has had text amended to it.
I have gotten that part working, the only problem is is that it is not dynamic, you have to manually created an offSet for however long the last line is. As such, I am trying to make a function that reads the last line until it finds a common element in all of the files this will be working with, and count how many bytes there were. This is what I have now for that:
int MeasureLastTag(CStdioFile* xmlFile)
{
TCHAR lastTag[1];
CString tagBracket = _T("");
xmlFile->Seek(0, CFile::end);
int count = 0;
while(tagBracket != _T("<")) //Go back two, read ahead one
{
xmlFile->Seek(-2, CFile::current);
xmlFile->Read(lastTag, 1);
tagBracket = lastTag;
count++;
}
return count;
}
However, this causes an infinite loop that I can't seem to shake. Any ideas on how to make it work?
Additional Information, this is a sample of the file.
<Station>
</Station>
I want it to read < /Station> until it gets to the <, counting along the way.
Changing TCHAR lastTag[1] to char lastTag[1] has solved the issue.
I have a binary file packing lots of files (something like a .tar), where I can found both binary and text files.
When processing in memory strings, carriage lines are usually '\n', but if I read the text part from this packed file, I get "\r\n". Therefore processing this text gives me errors.
Here is the code for reading the text from a binary file:
FILE* _fileDescriptor; // it's always open to improve performance
fopen_s(&_fileDescriptor, _filePath.string().c_str(), "rb");
char* data = new char[size + 1]; // size is a known and correct value
fseek(_fileDescriptor, begin, SEEK_SET); // begin is another known value, where the file starts inside the packed one
fread(data, sizeof(char), size, _fileDescriptor);
data[it->second.size] = '\0';
This gives me the right text into data, but the following code gives me error when reading an empty line:
istringstream ss(data); // create a stringstream to process it in another function
delete[] data; // free the data buffer
// start processing the file
string line;
getline(infile, line); // read an empty line
if(line.size() > 0) {
/*
enters here, because the "empty" line was "\r\n", and now the value of line is '\r', therefore line.size() == 1
*/
...
So, any advice to avoid the '\r'?
I edited it on Notepad++. Changing its configuration to use '\n' instead of '\r\n' as line carriage works, but I don't want to depend on this because other people can miss that, and it would be very hard to spot the problem if that happens.
Probably easiest to trim the '\r' characters out of your string and then discard blank lines. See this answer for approaches to trimming a std::string (I'm assuming that's what 'line' is):
What's the best way to trim std::string?
I've been stuck on this issue for a while. What I have here is a loop that will read a text file containing file names. The loop reads these lines one by one, and sets it into memory via the variable sFileName. sFileName is later called upon to load an image, and the program does this one by one as the loop loads it. The user then selects a tag for the image and loads the next one. The tag and the image file name are exported into another text file, named imgresults.txt. Now, the text file with the file names is a few thousand lines. So, in the case that the user has to exit the program and tries to continue later, the loop restarts, instead of leaving off at the point when the program was closed.
I am trying to find a way to have the loop start at that point. So far, I decided to use getline() to count how many lines are currently in imgresults.txt, as that will give the number of images that have already been run through the program. This number is stored in the variable "x". I've been doing a lot of research, but I just cannot find how to set a condition for the while loop to begin at line "x". Do you guys have any suggestions? Also, if you need any clarifications, please ask. I only included the code regarding the loop, as the code for loading the image and such is perfect fine.
int _tmain(int argc, _TCHAR* argv[])
{
int value = 0;
int nCounter = 0;
FILE* fIn = NULL;
char * sLine = new char[MAX_FILENAME_SIZE];
char * sFileName = new char [MAX_FILENAME_SIZE];
char * s = new char [MAX_FILENAME_SIZE];
#define ImgListFileName "path"
#define ImgRepository "path"
if ((fIn = fopen(ImgListFileName,"rt"))==NULL)
{
printf("Failed to open file: %s\n",ImgListFileName);
return nCounter;
}
ifstream imgresults;
imgresults.open ("imgresults.txt");
int x=0;
string line;
while(!imgresults.eof()) {
getline (imgresults, line);
x++;
}
srand (time(NULL));
cout << x;
while(!feof(fIn)){
memset(sLine,0,MAX_FILENAME_SIZE*sizeof(char));
memset(sFileName,0,MAX_FILENAME_SIZE*sizeof(char));
memset(s,0,MAX_FILENAME_SIZE*sizeof(char));
fgets(sLine,MAX_FILENAME_SIZE,fIn);
strncpy(s,sLine,65);
strcat(sLine,"\0");
strcat(sFileName,s);
printf (sFileName);
nCounter++;
}
Thanks in advance!
If you really want to use imgresults.txt as the information on where you should start from the input file, then the best you can do is to have a while loop to read x lines from the input file just before the while loop where you read the input file.
while (x--) {
fgets(sLine, MAX_FILENAME_SIZE, fIn);
}
Better solution would probably be to write state of processing to another file so that you would not have to read input file line by line, but you could immediately seek to a known offset in the file.
Use ifstream::tellg to retrieve and store the current position of the file when the programm was closed.
Use ifstream::seekg to restore that position when the porgramm restarts.
Before you read each line, save the current offsets in your input and output file to a separate file, seeking back to the beginning and overwriting the existing data each time.
When/if you restart, read the offsets from that file, seek to those points, and start working from there.
You can just read lines in parallel from both files and stop when you reach the end of results file. When the loop ends, you have already discarded the file names that were already processed.
ifstream results("results.txt");
ifstream names("names.txt");
if (results && names) {
std::string temp1, temp2;
while (getline(results, temp1) && getline(names, temp2)) ; /* do nothing */
}
if (names) {
// process the rest
}
Not the most efficient solution, but it saves you the hassle of saving offsets. Just make sure that before the very first processing the results file is completely empty (or doesn't exist at all), otherwise this code will skip the first line of names file.
I'm build a graphical program using visual c++ form. I'm trying to read a file to a string. The contents of the file is simple html code.
Now, if i create a blank project and create a .c file with this code:
FILE *f;
int tamanho;
char *asd;
f=fopen("mail.txt","r");
if(f==NULL)
erro("Erro abrir file");
fseek(f,0,SEEK_END);
tamanho=ftell(f);
rewind(f);
asd=(char *)malloc(tamanho+1);
fread(asd,1,tamanho,f);
It copies the whole to the string.
However if I create a windows form application and write the same code it only copies a few lines of my file.
fread() does not guarantee to read everything you ask for.
You need to check the return value to see how much was actually read.
You may need to do this in a loop until you have read everything you want.
size_t read = 0;
while(read != tamanho)
{
size_t amount = fread(asd + read,1,tamanho - read,f);
if (amount == 0)
{ // You may want to check for read errors here
}
read += amount;
}
Missing a while loop? That way u make sure u reach end of file properly
So I have a binary file that I create and initialize. If I set my pointer to seekg = 0 or seekp = 0, then I can overwrite the line of text fine. However if I jump ahead 26 bytes (the size of one line of my file and something I have certainly confirmed), it refuses to overwrite. Instead it just adds it before the binary data and pushes the old data further onto the line. I want the data completely overwritten.
char space1[2] = { ',' , ' '};
int main()
{
CarHashFile lead;
lead.createFile(8, cout);
fstream in;
char* tempS;
tempS = new char[25];
in.open("CarHash.dat", ios::binary | ios::in | ios::out);
int x = 2000;
for(int i = 0; i < 6; i++)
tempS[i] = 'a';
int T = 30;
in.seekp(26); //Start of second line
in.write(tempS, 6); //Will not delete anything, will push
in.write(space1, sizeof(space1)); //contents back
in.write((char *)(&T), sizeof(T));
in.write(space1, sizeof(space1));
in.write(tempS,6);
in.write(space1, sizeof(space1));
in.write((char *)&x, sizeof(x));
//Now we will use seekp(0) and write to the first line
//it WILL overwrite the first line perfectly fine
in.seekp(0);
in.write(tempS, 6);
in.write((char*) &x, sizeof(x));
in.write(tempS, 6);
in.write((char *) &T, sizeof(T));
return 0;
}
The CarHashFile is an outside class that creates a binary file full of the following contents when create file is invoked: "Free, " 1900 ", Black, $" 0.00f.
Everything enclosed in quotes was added as a string, 1900 as an int, and 0.00f as a float obviously. I added all of these through write, so I'm pretty sure it's an actual binary file, I just don't know why it only chooses to write over the first line. I know the file size is correct because if I set seekp = 26 it will print at the beginning of the second line and push it down. space was created to easily add the ", " combo to the file, there is also a char dol[1] = '$' array for simplicity and a char nl[1] = '\n' that lets me add a new line to the binary file (just tried removing that binary add and it forced everything onto one row, so afaik, its needed).
EDIT: Ok so, it was erasing the line all along, it just wasn't putting in a new line (kind of embarrassing). But now I can't figure out how to insert a newline into the file. I tried writing it the way I originally did with char nl[1] = { '\n' }. That worked when I first created the file, but won't afterwards. Are there any other ways to add lines? I also tried in << endl and got nothing.
I suggest taking this one step at a time. the code looks OK to me, but lack of error checking will mean any behavior could be happening.
Add error checks and reporting to all operations on in.
If that shows no issues, do a simple seek then write
result = in.pseek(26);
//print result
result = in.write("Hello World",10);
// print result
in.close();
lets know what happens
The end problem wasn't my understand of file streams. It was my lack of understanding of binary files. The newline screwed everything up royally, and while it could be added fine at one point in time, dealing with it later was a huge hassle. Once I removed that, everything else fell into place just fine. And the reason a lot of error checking or lack of closing files is there is because its just driver code. Its as bare bones as possible, I really didn't care what happened to the file at that point in time and I knew it was being opened. Why waste my time? The final version has error checks, when the main program was rewritten. And like I said, what I didn't get was binary files, not file streams. So AJ's response wasn't very useful, at all. And I had to have 25 characters as part of the assignment, no name is 25 characters long, so it gets filled up with junk. Its a byproduct of the project, nothing I can do about it, other than try and fill it with spaces, which just takes more time than skipping ahead and writing from there. So I chose to write what would probably be the average name (8 chars) and then just jump ahead 25 afterwards. The only real solution I could say that was given here was from Emile, who told me to get a Hex Editor. THAT really helped. Thanks for your time.