open() and write() functions in C

Question

I'm trying to write in a .txt file the content of the variable environ .

int archivo = open(argv[1], "rw");
int i=0;
while(environ[i]!=NULL){
    write(archivo, environ[i], 1024);
    i++;
}

The file is created but no content is added. Does anyone know why?

Answer 1

1. consult man 2 open to get the right arguments for open . It should be:

    open(argv[1], O_WRONLY | O_CREAT | O_TRUNC); 

2. You should only write ad much as you actually have:

    write(archivo, environ[i], strlen(environ[i])); 

3. You have to make sure that what you wrote actually left the buffer:

    size_t string_length = strlen(environ[i]); size_t wrote = 0; while (wrote < string_length) { size_t bytes_wrote = write(archivo, environ[i] + wrote, string_length - wrote); if (bytes_wrote >= 0) wrote += bytes_wrote; else { perror("write"); abort(); } } 

   write does not guarantee that all that you submit will be written.

Ideally you should look for the far more programmer friendly stdio calls fopen and fwrite .

FILE * fp = fopen(argv[1], "w");

// loop i
if (!fwrite(environ[i], strlen(environ[i]), 1, fp)) {
    perror("fwrite");
    abort();
}

Answer 2

I believe you've got to change your flags for opening a file. "rw" isn't for open(), it is for fopen().

open(argv[1], O_WRONLY);

I think is the minimum required for writing to a file using open

EDIT: I found a link http://pubs.opengroup.org/onlinepubs/009696899/functions/open.html