Thread: Text file versus Binary file

remember that fread and fwrite are basically used to read a block or chunk of data from a file. fread is used to read a block of data from the file. to write a block use fwrite. u can specify the no. of bytes to be read or written to the file, while using that fucntion. An example program which is gvien below is way of how to use a fread fucntion to read a text file all at one and place the contents of the text file into a buffer.

Code:

#include<stdio.h>

int main()
{
    FILE *fp;
    char *buff;
    int size;
    
    if((fp = fopen("test.txt","r"))==NULL)
    {
        printf("Error: File cannot be opened\n");
        getchar();
        return 1;
    }
    else
    {
        fseek(fp,0,SEEK_END);
        size = ftell(fp);
        fseek(fp,0,0);

        buff = malloc(size * sizeof(char));

        fread(buff,1,size,fp);
        *(buff+size)='\0';
        
        printf("%s",buff);

        fclose(fp);
        free(buff);
        
        getchar();
        return 0;
    }
}   

/*my output
this is test file
 
---- > My test.txt file <----
this is test file
*/

if u are using structure to store the reacords of the student and then writing onto the file. it better use binary file. so that u can read and write in terms of records. as i said earlier using fread/fwrite u can write/read a block of data.

ssharish2005

A few minor points:
1 - You don't open in binary mode. You should here. Depending on your OS, there may or may not be a difference between the two modes. There is in Windows.
2 - You use fseek with a text file. You shouldn't. Due to the above, you may or may not get the results you want when fseeking a text file. The problem is with newlines and the way they're handled between the two modes.
3 - You could have just used rewind, rather than using fseek to get to the start of the file.
4 - Your usage of ftell isn't all it seems either. Its return value is implementation dependant when used on text files.
5 - You never check the return value of ftell, which could be negative.
6 - Your usage of the ftell for the size to malloc is also incorrect. It's pure luck you didn't crash. You don't include room in your allocation for the nul character.


Quzah.

> and we can only use fread and fwrite..am i right?
There is no such thing as a "b" mode in Unix/Linux, it's all the same thing. The "b" is simply ignored if you use it on these platforms.

In microsoft land, the "b" mode stops the translation between '\n' and '\r\n'. This is important for applications trying to use fixed-length records, since this translation is going to affect the record length.

> Can we use fscanf and fprintf for a binary file?
Yes, but you would need to be careful about what applications you view the text file with. Most programmers editors, wordpad, word etc can cope with files with \n or \r\n endings. Simpler programs like notepad cannot.

> I see some programs usings fread and fwrite while their file is opened using text file
> modes,such as ,r,w,a..etc...will it work too?
Yes, they'll work fine on the normal operating systems.
They'll work fine too on windows as well, so long as you don't try and use fseek(). The fread() and fwrite() will perform \n to \r\n translation, but fseek() won't.

You can just have a loop of fwrite() calls to append one record after another in the file.