How to write an array to file in C

Question

I have a 2 dimensional matrix:

char clientdata[12][128];

What is the best way to write the contents to a file? I need to constantly update

Answer 1

Since the size of the data is fixed, one simple way of writing this entire array into a file is using the binary writing mode:

FILE *f = fopen("client.data", "wb");
fwrite(clientdata, sizeof(char), sizeof(clientdata), f);
fclose(f);

This writes out the whole 2D array at once, writing over the content of the file that has been there previously.

Answer 2

I would rather add a test to make it robust ! The fclose() is done in either cases otherwise the file system will free the file descriptor

int written = 0;
FILE *f = fopen("client.data", "wb");
written = fwrite(clientdata, sizeof(char), sizeof(clientdata), f);
if (written == 0) {
    printf("Error during writing to file !");
}
fclose(f);

Answer 3

How incredibly simple this issue turned out to be... The example given above handle characters, this is how to handle an array of integers...

/* define array, counter, and file name, and open the file */
int unsigned n, prime[1000000];
FILE *fp;
fp=fopen("/Users/Robert/Prime/Data100","w");
prime[0] = 1;  /* fist prime is One, a given, so set it */
/* do Prime calculation here and store each new prime found in the array */
prime[pn] = n; 
/* when search for primes is complete write the entire array to file */
fwrite(prime,sizeof(prime),1,fp); /* Write to File */

/* To verify data has been properly written to file... */
fread(prime,sizeof(prime),1,fp); /* read the entire file into the array */
printf("Prime extracted from file Data100: %10d \n",prime[78485]); /* verify data written */
/* in this example, the 78,485th prime found, value 999,773. */

For anyone else looking for guidance on C programming, this site is excellent...

Refer: [https://overiq.com/c-programming/101/fwrite-function-in-c/