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
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.
EDIT: Problem solved! Turns out Windows 7 wont let me read/ write to files without explicitly running as administrator. So if i run as admin it works fine, if i dont i get the weird results i explain below.
I've been trying to get a part of a larger program of mine to read a file.
Despite trying multiple methods(istream::getline, std::getline, using the >> operator etc) All of them return with either /0, blank or a random number/what ever i initialised the var with.
My first thought was that the file didn't exist or couldn't be opened, however the state flags .good, .bad and .eof all indicate no problems and the file im trying to read is certainly in the same directory as the debug .exe and contains data.
I'd most like to use istream::getline to read lines into a char array, however reading lines into a string array is possible too.
My current code looks like this:
void startup::load_settings(char filename[]) //master function for opening a file.
{
int i = 0; //count variable
int num = 0; //var containing all the lines we read.
char line[5];
ifstream settings_file (settings.inf);
if (settings_file.is_open());
{
while (settings_file.good())
{
settings_file.getline(line, 5);
cout << line;
}
}
return;
}
As said above, it compiles but just puts /0 into every element of the char array much like all the other methods i've tried.
Thanks for any help.
Firstly your code is not complete, what is settings.inf ?
Secondly most probably your reading everything fine, but the way you are printing is cumbersome
cout << line; where char line[5]; be sure that the last element of the array is \0.
You can do something like this.
line[4] = '\0' or you can manually print the values of each element in array in a loop.
Also you can try printing the character codes in hex for example. Because the values (character codes) in array might be not from the visible character range of ASCII symbols. You can do it like this for example :
cout << hex << (int)line[i]
I am basically trying to reverse the contents of a text file. When I run this code, nothing happens. Code:
getArguments();
stringstream ss;
ss << argument;
string fileName;
ss >> fileName;
fstream fileToReverse(fileName);
if (fileToReverse.is_open()) {
send(sock, "[*] Contents is being written to string ... ", strlen("\n[*] Contents is being written to string ... "), 0);
string line;
string contentsOfFile;
while (getline(fileToReverse, line)) {
contentsOfFile.append(line);
line = "\0";
}
send(sock, "done\n[*] File is being reversed ... ", strlen("done\n[*] File is being reversed ... "), 0);
string reversedText(contentsOfFile.length(), ' ');
int i;
int j;
for(i=0,j=contentsOfFile.length()-1;i<contentsOfFile.length();i++,j--) {
reversedText[i] = contentsOfFile[j];
}
contentsOfFile = "\0";
fileToReverse << reversedText;
fileToReverse.close();
send(sock, "done\n", strlen("done\n"), 0);
}
fileName is created from user input, and I know that the file exists. It just doesn't do anything to the file. If anyone has any ideas that they would like to share that would be great.
UPDATE:
I now can write reversedText to the file but how can I delete all of the files contents?
In this particular case, when you have read all the input content, your file is in an "error state" (eof and fail bits set in the status).
You need to clear that with fileToReverse.clear();. Your file position will also be at the end of the file, so you need to use fileToReverse.seekp(0, ios_base::beg) to set the position to the beginning.
But I, just as g-makulik, prefer to have two files, one for input and one for output. Saves a large amount of messing about.
When you need to debug something like this - saying "all the functions are being run and all the variables are being created, and it compiled without any warnings" isn't really debugging.
Debugging - this doesn't work. Remove bits until you find what doesn't work. Like you said - all variables are what you expect them. So... try and see if, for example, the way you read and write from a file works. Just write a small program that opens a file like you open it, reads from it like you do and then writes... whatever back into it in the same way you do. See if that works.
In other words, try and find the smallest program that reproduces what you see.
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.
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