1. The difference between w and wb in fopen

The black part is the program, the white part is the annotation, and part of the content is reproduced in the sub-network.

1. Header file

#include <cstdio>

#include <unistd.h>

2. Open the file

typedef struct {
    unsigned char head[2];
    unsigned char status;
    unsigned char crc8;
    unsigned short datalen;
}BACKUP_HEAD;

    

BACKUP_HEAD bhead = { 'A' , 'B' , 0x0A , 0x0A , 0x0A };

FILE *fp = (FILE *)0x00;
    if(!(fp = fopen("/dev/mtdblock4", "w+"))) return -0x01;

w is to open the file in text mode, wb is to open the file in binary mode, when opening the file in text mode, every time the fwrite function encounters a 0x0A,

Just add 0x0D in front of it. Do not add other content.

Such as:

    

fwrite((char *)&bhead,sizeof(BACKUP_HEAD),1,fp);

Our structure defines three 0x0A, so when operating with a text file, the content of 0x0A will not be written, but it is equivalent to carriage return and line feed.

result:

Replace w with wb+

FILE *fp = (FILE *)0x00;
    if(!(fp = fopen("/dev/mtdblock4", "wb+"))) return -0x01;

rewrite

fwrite((char *)&bhead,sizeof(BACKUP_HEAD),1,fp); the result is

The binary mode will output the data to the file as it is stored in the memory.

Summarize:

(1) Write and read should be consistent. If writing is in text mode, it should be in text mode when reading; if writing in binary mode, it should be in binary mode when reading.

(2) Whether it is a text file or a binary file, if the binary method is used for reading and writing, there will be no error.