What is Binary File I/O in C?

    in_out = fopen("test.txt", "a+");
 
    float val = 10.0/3.0, dval;

    fprintf(in_out, "%f", val);

    fscanf(in_out, "%f", &dval);

    val == dval;

/* binary_io.c -- */
/* size_t fread(void *buffer, size_t size, size_t count, FILE * stream) */
/* size_t fwrite(void *buffer, size_t size, size_t count, FILE * stream) */
 
#include <stdio.h>
#include <stdlib.h>
#define TEXTSIZE 20
#define SIZE 10
 
int main(void)
{
    int i, n_values;
    long current, changed, bcurrent, bchanged;
    float fval;
    FILE *text_in_out, *binary_in_out;
    char tf_name[TEXTSIZE], bf_name[TEXTSIZE];
 
    float fvalues[SIZE] = {2.0, 10.9/5.4, 23.45, 1.23/7, 0.34,
                      5.67, 10.87, 2.3, 12.0, 6.67};
 
    float dvalues[SIZE]; /* buffer for duplicate floats */
 
    printf("user, give name for text file:");
    scanf("%s", tf_name);
 
    printf("\n");
 
    /* open text file in update mode */
    text_in_out = fopen(tf_name, "a+");
    if (text_in_out == NULL) {
        perror("File Open");
        exit(EXIT_FAILURE);
    }
 
    /* write floats to text file named tf_name */
    for (i = 0; i < SIZE; i++)
        fprintf(text_in_out, "%f\n", fvalues[i]);
 
    /* let's check current position in text file */
    current = ftell(text_in_out);
    printf("Next read or write will occur at offset:%ld from the "
           "beginning.\n", current);
 
    /* call fseek() to set to read from beginning */
    fseek(text_in_out, -current, SEEK_END);
 
    /* changed position in text file */
    changed = ftell(text_in_out);
    printf("Next read or write will occur at offset:%ld from the "
           "beginning.\n", changed);
 
    /* before attempt to read from the file, flush text_in_out stream */
    fflush(text_in_out);
 
    /* perform reading from the file */
    /* attempt to read floating values from the file back to program */
    printf("\nfloat values:\n");
    for (i = 0; i < SIZE; i++) {
        fscanf(text_in_out, "%f", &fval);
        printf("%f\n", fval);
    }
 
    /* let's write float values efficiently in binary */
    printf("\nLet's write float values in binary...\n");
    printf("user, give name for binary file:");
    scanf("%s", bf_name);
 
    printf("\n");
 
    /* open binary file in update mode */
    binary_in_out = fopen(bf_name, "ab+");
    if (binary_in_out == NULL) {
        perror("File Open");
        exit(EXIT_FAILURE);
    }
 
    /* write float values to binary file using fwrite() */
    /*
     * int fwrite(void *buffer, size_t size_of_element,
                    size_t no_of_elements, FILE *stream);
     */
    n_values = fwrite(fvalues, sizeof(float), SIZE, binary_in_out);
    printf("No of values written to binary file \"%s\" is %d.\n",
            bf_name, n_values);
 
    /* flushing stream binary_in_out */
    fflush(binary_in_out);
 
    /* let's check current position in binary file */
    bcurrent = ftell(binary_in_out);
    printf("Binary File: Next read or write will occur at offset:%ld "
           "from the beginning.\n", bcurrent);
 
    /* let's set to read from beginning in binary file using fseek() */
    fseek(binary_in_out, -bcurrent, SEEK_END);
 
    bchanged = ftell(binary_in_out);
    printf("Binary File: Next read or write will occur at offset:%ld "
           "from the beginning.\n", bchanged);
 
    /* let's read floats from binary file back to buffer in program */
    /*
     * int fread(void *buffer, size_t size_of_element,
                 size_t no_of_element, FILE *stream);
     */
    n_values = fread(dvalues, sizeof(float), n_values, binary_in_out);
    printf("No of values read into buffer \'dvalues\' from binary file "
            "\"%s\" is %d.\n", bf_name, n_values);
 
    /* let's compare fvalues and dvalues */
    printf("\nLet's compare float values in buffers: fvalues and "
           "dvalues:\n");
    for (i = 0; i < SIZE; i++) {
        if (fvalues[i] == dvalues[i])
            printf("fvalues[%d] and dvalues[%d] is SAME.\n", i, i);
    }
 
    return 0;
}

user, give name for text file:tfile
 
Next read or write will occur at offset:93 from the beginning.
Next read or write will occur at offset:0 from the beginning.
 
float values:
2.000000
2.018518
23.450001
0.175714
0.340000
5.670000
10.870000
2.300000
12.000000
6.670000
 
Let us write float values in binary...
user, give name for binary file:bfile
 
No of values written to binary file "bfile" is 10.
Binary File: Next read or write will occur at offset:40 from the beginning.
Binary File: Next read or write will occur at offset:0 from the beginning.
No of values read into buffer 'dvalues' from binary file "bfile" is 10.
 
Let's compare float values in buffers: fvalues and dvalues:
fvalues[0] and dvalues[0] is SAME.
fvalues[1] and dvalues[1] is SAME.
fvalues[2] and dvalues[2] is SAME.
fvalues[3] and dvalues[3] is SAME.
fvalues[4] and dvalues[4] is SAME.
fvalues[5] and dvalues[5] is SAME.
fvalues[6] and dvalues[6] is SAME.
fvalues[7] and dvalues[7] is SAME.
fvalues[8] and dvalues[8] is SAME.
fvalues[9] and dvalues[9] is SAME.