Wrting "Null" Values into File

[eng01015]

Hi to all,

I need to write data into a file of such format

wd (I can do this)
ht (I can do this)
x x x x x x x ... x (How do I do this?)

where the x's represent NULL char values.

Using fprintf(filename, "%c", ...) or something like that, how can I print the NULL values?

Thx in Adv,
Julian.

[raimo]

Using fprintf(filename, "%c", ...) or something like that, how can I print the NULL values?

You cannot use fprintf for that purpose because by definition it writes the string without trailing '\0':s.
As you use C the fwrite function should work for you.

fwrite man page:

size_t fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream);

The function fwrite() writes nmemb objects, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.

The function fwrite() returns a value less than nmemb only if a write error has occurred.

[eng01015]

hi again,

May I know what would the 'NULL' chars look like if i write it to a .txt file? Is it just blank spaces, or should it be "squares"?

Thx again!
Julian.

[raimo]

May I know what would the 'NULL' chars look like if i write it to a .txt file? Is it just blank spaces, or should it be "squares"?

It depends on how you show them on the screen in your program or which editor you use to open the file.
For example, editor called VIM on Unix will show "^@" marks meaning NULL in a file. I'm kinda interested to know how windows notepad handles that situation, try this program:

Code: Select all

#include <stdio.h>

int main () {
        char ptr[] = "this is a \0string\0";
        FILE *fp;
        fp=fopen("string.txt","w");
        fwrite(ptr,1,18,fp);
        fclose(fp);
}


Run it and open "string.txt" using Notepad and see what happens. Try changing "w" to "wb" and see what's the difference. On Unix this makes no difference at all, binary and text are handled the same way.