struct結構

struct array寫入binary file

size_t fwrite(const void *buf, size_t size, size_t n, FILE *fp)
size_t fread(void *ptr, size_t, size_t n, FILE *fp)

• 第一個參數傳的是要讀出或要寫入的起始位址，所以傳入陣列名稱即可。
  • 第二個參數為每一個寫入/讀出資料的大小，由於一次寫入/讀取一個struct，所以為sizeof(struct Student)或sizeof(Student)
  • 第三個參數為寫入/讀出的數目，故傳入array size。
  • 第四個參數為文字檔的file handler。

#define NAME_LEN 11
#define ARRAY_SIZE 3

struct Student {
    int  id;
    char name[NAME_LEN];
};

typedef struct Student Student;

int main() {
    Student student0[ARRAY_SIZE]; // struct array for write
    Student student1[ARRAY_SIZE]; // struct array for read
    FILE *fp;                     // file handle
    int i;                        // for loop counter

    // input struct array
    student0[0].id = 1;
    strcpy(student0[0].name, "clare");

    student0[1].id = 2;
    strcpy(student0[1].name, "jingyi");

    student0[2].id = 3;
    strcpy(student0[2].name, "jessie");

    // open binary file [write binary]
    if (!(fp = fopen("library.dat", "wb")))
        return -1;

    // size_t fwrite(const void *buf, size_t size, size_t n, FILE *fp)
    fwrite(student0, sizeof(Student), ARRAY_SIZE, fp);

    fclose(fp); // close file

    // open binary file [read binary]
    if (!(fp = fopen("library.dat", "rb")))
        return -1;

    // size_t fread(void *ptr, size_t, size_t n, FILE *fp)
    fread(student1, sizeof(Student), ARRAY_SIZE, fp);
    for(i = 0; i != ARRAY_SIZE; ++i) {
        printf("%d\n", student1[i].id);
        printf("%s\n", student1[i].name);
    }
    fclose(fp);
}