[TOC]

fwrite

size_t fwrite ( const void * ptr, size_t size, size_t count, FILE * stream );

• ptr：指向保存數據的指針；
• size：每個數據類型的大小
• count：數據的個數
• stream：文件指針
• return 函數返回寫入數據的個數

int write(const char *path) {
    FILE *file = fopen(path, "wb");
    if (file == NULL) {
        return 0;
    }
    int arr[4] = {0x00000012, 0x00001234, 0x00123456, 0x12345678};
    for (int i = 0; i < 4; i++) {
        fwrite(&arr[i], sizeof(int), 1, file);
    }
    fclose(file);
    return 1;
}

查看輸出的文件，看到數據的存儲是小端對齊

1.png

w wb的區別

wb 打開或新建一個二進制文件，在POSIX系統，包括Linux都會忽略該字符。windows文本文件打開時寫入\n，會自動加上\r變成\r\n。而已二進制方式打開則不會加上\r。

int write(const char *path) {
    FILE *file = fopen(path, "wb+");
//    FILE *file = fopen(path, "w");
    if (file == NULL) {
        return 0;
    }
    char *p = "abc\n1234";
    int len = fwrite(p, sizeof(char), strlen(p), file);
    printf("write len=%d\n", len);
    fclose(file);
    return 1;
}

使用wb+時候結果為:

write len=8
-------------
abc
12341234
read  length=8

使用w打開時，結果為：

write len=8
-------------
abc
1234123
read  length=9

fread

int read(const char *path) {
    FILE *file = fopen(path, "rb");
    if (file == NULL) {
        return 0;
    }
    int len = 0;
    int total = 0;
    char buf[5] = {0};
    while (!feof(file)) {
        len = fread(buf, sizeof(char), 4, file);
        printf("%s", buf, len);
        total += len;
    }
    printf("\nread  length=%d", total);
    fclose(file);
    return 1;
}

注意：fread返回成功有效的讀取的item元素的個數。

這里修改寫下代碼：

#include <stdio.h>
#include <mem.h>

char *PATH1 = "D:\\code\\CProject\\FileByte\\1";

int read(const char *);

int write(const char *);

int main() {
    write(PATH1);
    printf("-------------\n");
    read(PATH1);
    return 0;
}

int write(const char *path) {
//    FILE *file = fopen(path, "wb+");
    FILE *file = fopen(path, "w");
    if (file == NULL) {
        return 0;
    }
    char *p = "abc\n1234";
    int len = fwrite(p, sizeof(char), strlen(p), file);
    printf("write len=%d\n", len);
    fclose(file);
    return 1;
}

int read(const char *path) {
    FILE *file = fopen(path, "rb");
    if (file == NULL) {
        return 0;
    }
    int len = 0;
    int total = 0;
    //使用short
    short buf[20] = {0};
    while (!feof(file)) {
        len = fread(buf, sizeof(short), 20, file);
        for (int i = 0; i < len + 2; i++) {
            printf("%x-", buf[i]);
        }
        total += len;
    }
    printf("\nread  length=%d", total);
    fclose(file);
    return 1;
}

結果為：

write len=8
-------------
6261-d63-310a-3332-34-0-
read  length=4

總共9個字節，而實際有效讀入了4個short。

2.png