[SOLVED] fprintf problem (ofstream)

robertodb · 09-21-2011, 10:37 AM

I wrote a program that creates a text file with some letters using ofstream. Now I would like to format the text so that the letters are written in groups of 5 and the rows are all the same length( i.e. LINUXQUESTIONS becomes LINUX QUEST IONS). To do this the fprintf function seemed the most appropriate. in the following example I use integers, but it is just an example.

Code:

#include <string>
#include <iomanip>
#include <fstream>
#include <cstdio>

using namespace std;

int main()
{
    ofstream f;
    
    f.open("testo.txt");
    
    for(int i = 0; i < 21; i++)
    {
            f << i;  
            }
            
    f.close(); //to simulate file already created
    
    FILE *file;
    int number;
    file = fopen("testo.txt", "r+");
    if (file==NULL) perror ("Error opening file");
    else
    {
        do {
           number = fgetc (file);
           fprintf(file, "%-5.5i", number);
        } while (number != EOF);
     }
     fclose(file);
     return 0;
}

can this method work? or there is some function that I can use directly when creating the file with ofstream?
please help

Snark1994 · 09-21-2011, 10:53 AM

Forgive me if I'm being foolish, but when you say

Quote:

or is there some function that I can use directly when creating the file with ofstream?

surely you could just write five characters, write a space, write another five, and so on until you run out of characters? That would be far easier than messing with the file after it's been created. The code you have there doesn't work (as you hopefully know); if you did want your approach to work, you'd have to use a temporary file (you're currently doing weird things by reading and writing) and you would again count five characters and then add a space, rather than playing with padding integers...

In the vein of the first suggestion, the following works:

Code:

#include <string>
#include <iomanip>
#include <fstream>
#include <cstdio>

using namespace std;

int main() {
    //Your code:
    ofstream f;
    
    f.open("testo.txt");
    
    for(int i = 0; i < 21; i++) {
                f << i;  
        }
            
    f.close(); //to simulate file already created
    
    //My code:
    FILE *in;
    FILE *out;
    in = fopen("testo.txt", "r");
    out = fopen("out.txt", "w");
    if (in==NULL) {
        perror ("Error opening file");
    } else {
        char character;
        do {
            for(int i=0;i<5 && character != EOF;i++){
                character = fgetc (in);
                fprintf(out, "%c", character);
            }
            fprintf(out, " ");
        } while (character != EOF);
     }
     fclose(in);
     fclose(out);
     return 0;
}

I used C-style file input/output because you did (though not for the first bit?), but it would be "better" to use C++ style I/O if you're using C++ (which you are if you're using string)

Hope this helps,

robertodb · 09-21-2011, 11:20 AM

Quote:

surely you could just write five characters, write a space, write another five, and so on until you run out of characters? That would be far easier than messing with the file after it's been created.

this is the piece of original code

Code:

void Vigenere::encode(string plaintext, string encoded_f){
       ofstream f; 
                     
       TextErase();
       LoadText(plaintext); //load a text file in text (vector<string>)
       
       f.open(encoded_f.c_str());
       if(!f.is_open()){
           cout << "Error creating file: " << encoded_f << " !" << endl;
           return;
       }
       
       int* index_k = new int[key.length()]; //key indexs array
       for(int i = 0; i < key.length(); i++){
               for(int j = 0; j < 21; j++){
                       if(key[i] == ALPH[j])
                       index_k[i] = j;
               }
       }
       
       int passcnt = 0;
       for(int i = 0; i < text.size(); i++){ 
               for(int j = 0; j < text[i].size(); j++){ 
                    int* index_t = new int[text[i].length()];
                         for(int k = 0; k < 21; k++){ 
                              if(text[i][j] == ALPH[k])
                              index_t[j] = k;
                         }
                    char ch = ALPH[(index_t[j] + index_k[passcnt])%21];
                    f << ch;
                    passcnt++;
                    if(passcnt > (key.length() - 1))
                    passcnt = 0;
                    
                    delete[] index_t; 
               }
               f << "\n";
       }
       f.close();
       delete[] index_k;
       return;
}

how can I change this to do what you say? by the way, you're completely right, this way seems to be easier, but after a day spent at the computer, the brain no longer works well...

Snark1994 · 09-21-2011, 05:06 PM

I will admit to being both rather tired and in a state of mild intoxication, so I will have another look at it tomorrow... However, it looks like if you change it to:

Code:

void Vigenere::encode(string plaintext, string encoded_f){
//     ...
       int numberOfCharsPrinted = 0;
       
       int passcnt = 0;
       for(int i = 0; i < text.size(); i++){ 
               for(int j = 0; j < text[i].size(); j++){ 
//      ...
                    char ch = ALPH[(index_t[j] + index_k[passcnt])%21];
                    if (numberOfCharsPrinted == 5){
                        f << ' ';
                        numberOfCharsPrinted = 0;
                    }
                    f << ch;
                    passcnt++;
                    numberOfCharsPrinted++;
//      ...
       return;
}

...where "..." represents code which should be included but which I've omitted to make the changes that I've made more clear

Hope this helps,

robertodb · 09-22-2011, 02:08 AM

thank you very much. I can't believe...it works!!!

robertodb · 09-22-2011, 02:44 AM

ok it works, but there's something I can't understand in the output. the content of a text file is

Code:

roberto di bernardo
file di testo
prova criptografica

and, after encoding, the output file is

Code:

LDCIL PDUZC ILHOL RP
LCF SUZUI MPD
HG PCRVG CEUSA NOZZD E

while I'd like to have something like this

Code:

LDCIL PDUZC ILHOL RP
LCFSU ZUIMP D
HGPCR VGCEU SANOZ ZDE

how can I fix that? I swear, this will be the last question...I'll not bother you anymore, at least for the next two or three weeks.

Snark1994 · 09-22-2011, 08:36 AM

Right, all you need to do is put another "numberOfCharsPrinted = 0;" after "f << '\n';"; if you look at your output it is putting a space after every 5 characters, but sometimes the linebreak occurs in the middle. Setting numberOfCharsPrinted to 0 after every linebreak means everything will come out in groups of 5.

Don't worry about asking questions, it is a real pleasure to be able to help someone, especially someone who's polite

Buona fortuna!

robertodb · 09-22-2011, 09:23 AM

ok, now it's perfect, just like I wanted.
grazie