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.
Related
I'm trying to create a program that encrypts files based on how Nazi Germany's Enigma machine worked, but without the flaw :P.
I have a function that gets a character at n point in a file, but when it returns a return character and I cout << it, it's like it hit enter twice.
IE if I loop cout-ing from i++ points in a file the individual lines in the terminal appear separated
by more returns
than one.
Here's the function:
char charN(string pathOf, int pointIn){
char r = NULL;
// NULL so I can tell when it doesn't return a character.
int sizeOf; //to store the found size of the file.
ifstream cf; //to store the Character Found.
ifstream siz; //used later to get the size of the file
siz.open(pathOf.c_str());
siz.seekg(0, std::ios::end);
sizeOf = siz.tellg(); // these get the length of the file and put it in sizeOf.
cf.open(pathOf.c_str());
if(cf.is_open() && pointIn < sizeOf){ //if not open, or if the character to get is farther out than the size of the file, let the function return the error condition: 'NULL'.
cf.seekg(pointIn); // move to the point in the file where the character should be, get it, and get out.
cf.get(r);
cf.close();
}
return r;
}
It works correctly if I use cout << '\n', but what's different about returns from a file and '\n'?
Or is there something else I'm missing?
I've been googling about but I can't find anything remotely similar to my problem, thanks in advance.
I'm using Code::Blocks 13.12 as my compiler if that matters.
Is this is on a windows machine? In windows new lines in text files are representing by \r\n.
\r = carriage return
\n = line feed
It's possible that you are couting each one separately and that the output buffer is creating a new line for each one.
I have a small program, that is meant to copy a small phrase from a file, but it appears that I am either misinformed as to how seekg() works, or there is a problem in my code preventing the function from working as expected.
The text file contains:
//Intro
previouslyNoted=false
The code is meant to copy the word "false" into a string
std::fstream stats("text.txt", std::ios::out | std::ios::in);
//String that will hold the contents of the file
std::string statsStr = "";
//Integer to hold the index of the phrase we want to extract
int index = 0;
//COPY CONTENTS OF FILE TO STRING
while (!stats.eof())
{
static std::string tempString;
stats >> tempString;
statsStr += tempString + " ";
}
//FIND AND COPY PHRASE
index = statsStr.find("previouslyNoted="); //index is equal to 8
//Place the get pointer where "false" is expected to be
stats.seekg(index + strlen("previouslyNoted=")); //get pointer is placed at 24th index
//Copy phrase
stats >> previouslyNotedStr;
//Output phrase
std::cout << previouslyNotedStr << std::endl;
But for whatever reason, the program outputs:
=false
What I expected to happen:
I believe that I placed the get pointer at the 24th index of the file, which is where the phrase "false" begins. Then the program would've inputted from that index onward until a space character would have been met, or the end of the file would have been met.
What actually happened:
For whatever reason, the get pointer started an index before expected. And I'm not sure as to why. An explanation as to what is going wrong/what I'm doing wrong would be much appreciated.
Also, I do understand that I could simply make previouslyNotedStr a substring of statsStr, starting from where I wish, and I've already tried that with success. I'm really just experimenting here.
The VisualC++ tag means you are on windows. On Windows the end of line takes two characters (\r\n). When you read the file in a string at a time, this end-of-line sequence is treated as a delimiter and you replace it with a single space character.
Therefore after you read the file you statsStr does not match the contents of the file. Every where there is a new line in the file you have replaced two characters with one. Hence when you use seekg to position yourself in the file based on numbers you got from the statsStr string, you end up in the wrong place.
Even if you get the new line handling correct, you will still encounter problems if the file contains two or more consecutive white space characters, because these will be collapsed into a single space character by your read loop.
You are reading the file word by word. There are better methods:
while (getline(stats, statsSTr)
{
// An entire line is read into statsStr.
std::string::size_type posn = statsStr.find("previouslyNoted=");
// ...
}
By reading entire text lines into a string, there is no need to reposition the file.
Also, there is a white-space issue when reading by word. This will affect where you think the text is in the file. For example, white space is skipped, and there is no telling how many spaces, newlines or tabs were skipped.
By the way, don't even think about replacing the text in the same file. Replacement of text only works if the replacement text has the same length as the original text in the file. Write to a new file instead.
Edit 1:
A better method is to declare your key strings as array. This helps with positioning pointers within a string:
static const char key_text[] = "previouslyNoted=";
while (getline(stats, statsStr))
{
std::string::size_type key_position = statsStr.find(key_text);
std::string::size_type value_position = key_position + sizeof(key_text) - 1; // for the nul terminator.
// value_position points to the character after the '='.
// ...
}
You may want to save programming type by making your data file conform to an existing format, such as INI or XML, and using appropriate libraries to parse them.
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]
UPDATE: Yes, answered and solved. I also then managed to find the issue with the output that was the real problem I was having. I had thought the substring error was behind it, but I was wrong, as when that had been fixed, the output issue persisted. I found that it was a simple mix up in the calculations. I had been subtracting 726 instead of 762. I could've had this done hours ago... Lulz. That's all I can say... Lulz.
I am teaching myself C++ (with the tutorial from their website). I have jumped ahead time to time when I have needed to do something I cannot with what I have learned so far. Additionally, I wrote this relatively quickly. So, if my code looks inelegant or otherwise unacceptable at a professional level, please do excuse that for now. My only current purpose is to get this question answered.
This program takes each line of a text file I have. Note that the text file's lines look like this:
.123.456.789
It has 366 lines. The program I first wrote to deal with this had me input each of the three numbers for each line manually. As I'm sure you can imagine, that was extremely inefficient. This program's purpose is to take each number out of the text file and perform functions and output the results to another text file. It does this per line until it reaches the end of the file.
I have read up more on what could cause this error, but I cannot find the cause of it in my case. Here is the bit of the code that I believe to contain the cause of the problem:
int main()
{
double a;
double b;
double c;
double d;
double e;
string search; //The string for lines fetched from the text file
string conversion;
string searcha; //Characters 1-3 of search are inserted to this string.
string searchb; //Characters 5-7 of search are inserted to this string.
string searchc; //Characters 9-11 of search are inserted to this string.
string subsearch; //Used with the substring to fetch individual characters.
string empty;
fstream convfil;
convfil.open("/home/user/Documents/MPrograms/filename.txt", ios::in);
if (convfil.is_open())
{
while (convfil.good())
{
getline(convfil,search); //Fetch line from text file
searcha = empty;
searchb = empty;
searchc = empty;
/*From here to the end seems to be the problem.
I provided code from the beginning of the program
to make sure that if I were erring earlier in the code,
someone would be able to catch that.*/
for (int i=1; i<4; ++i)
{
subsearch = search.substr(i,1);
searcha.insert(searcha.length(),subsearch);
a = atof(searcha.c_str());
}
for (int i=5; i<8; ++i)
{
subsearch = search.substr(i,1);
searchb.insert(searchb.length(),subsearch);
b = atof(searchb.c_str());
}
for (int i=9; i<search.length(); ++i)
{
subsearch = search.substr(i,1);
searchc.insert(searchc.length(),subsearch);
c = atof(searchc.c_str());
}
I usually teach myself how to get around these issues when they come up by looking at references and problems other people may have had, but I couldn't find anything that helped me in this instance. I have tried numerous variations upon this, but as the issue has something to do with the substring and I couldn't get rid of the substring in any of these variations, all returned the same error and the same result in the output file.
This is a problem:
while (convfil.good()) {
getline(convfil,search); //Fetch line from text file
You test for failure before you do the operation that can fail. When getline does fail, you're already inside the loop.
As a result, your code tries to process an invalid record at the end.
Instead try
while (getline(convfil,search)) { //Fetch line from text file
or even
while (getline(convfil,search) && search.length() > 9) {
which will also stop without error if there's a blank line at the end of the file.
It's possible you are reading a blank line at the end of the file and trying to process it.
Test for an empty string before processing it.
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.