File I/O – Binary Files

Binary files store raw bytes without newline translation.

FILE *fp = fopen("data.bin", "wb");
int vals[5] = {10,20,30,40,50};
fwrite(vals, sizeof vals, 1, fp);
fclose(fp);

Reading:

FILE *fp = fopen("data.bin", "rb");
int vals[5];
fread(vals, sizeof vals, 1, fp);

Always check the return of fwrite/fread for the number of items written/read.

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📚 Example: Storing a Struct to Disk

#include <stdio.h>
#include <stdint.h>

struct Record {
    uint32_t id;
    double   value;
    char     name[16];
};

int main(void) {
    struct Record r = { 42, 3.1415, "sample" };
    FILE *f = fopen("record.bin", "wb");
    if (!f) return 1;
    fwrite(&r, sizeof r, 1, f);
    fclose(f);
    return 0;
}