基于正点原子的库函数版本的FATS文件系统，实现向文件写入字符串，读取文件内容，这里是指txt文件，其余文件其实也一样，读取成字节。

#include "led.h"
#include "delay.h"
#include "sys.h"
#include "usart.h"
#include "key.h"

#include "MMC_SD.h"

#include "ff.h"
#include "exfuns.h"
#include "fattester.h"
#include "malloc.h"
#include "string.h"


extern FATFS *fs[2];
extern FIL *file;          //文件1
extern UINT br, bw;         //读写变量

// 将字符串写入txt文件
void write_to_txt(const char *filename, const char *str) {
    FRESULT res;

    res = f_open(file, filename, FA_CREATE_ALWAYS | FA_WRITE);  // 打开或创建文件
    if (res != FR_OK) {
        printf("Failed to open file: %d\r\n", res);
        return;
    }

    res = f_write(file, str, strlen(str), &bw);  // 写入数据
    if (res != FR_OK) {
        printf("Failed to write file: %d\r\n", res);
        f_close(file);
        return;
    }

    res = f_close(file);  // 关闭文件
    if (res != FR_OK) {
        printf("Failed to close file: %d\r\n", res);
        return;
    }

    printf("Write successfully, %u bytes written\r\n", bw);
}

void append_to_file(const char *filename, const char *data) {
    FRESULT res;

    res = f_open(file, filename, FA_WRITE | FA_OPEN_ALWAYS);  // 打开文件
    if (res != FR_OK) {
        printf("Failed to open file: %d\r\n", res);
        return;
    }

    res = f_lseek(file, file->fsize);  // 将写入指针定位到文件末尾
    if (res != FR_OK) {
        printf("Failed to seek file: %d\r\n", res);
        f_close(file);
        return;
    }

    res = f_write(file, data, strlen(data), &bw);  // 写入数据到文件末尾
    if (res != FR_OK || bw == 0) {
        printf("Failed to write file: %d\r\n", res);
        f_close(file);
        return;
    }

    res = f_close(file);  // 关闭文件
    if (res != FR_OK) {
        printf("Failed to close file: %d\r\n", res);
        return;
    }
}

#define MAX_LINE_SIZE 100

// 动态读取txt文件的行并进行处理
void process_lines_from_txt(const char *filename) {
    FRESULT res;
    char line[MAX_LINE_SIZE];

    res = f_open(file, filename, FA_READ);  // 打开文件
    if (res != FR_OK) {
        printf("Failed to open file: %d\r\n", res);
        return;
    }

    while (f_gets(line, MAX_LINE_SIZE, file) != NULL) {  // 按行读取文件内容
        printf("%s", line);  // 打印读取的内容

        // 这里可以对每一行进行处理，例如调用其他函数进行处理

        // 读取下一行之前可以进行必要的等待或延时操作

    }

    res = f_close(file);  // 关闭文件
    if (res != FR_OK) {
        printf("Failed to close file: %d\r\n", res);
        return;
    }
}

int main(void) {
    char str[] = "Hello, world!";
    char str1[] = "\r\nHello, world!";

    u32 total, free;
    u8 t = 0;
    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);// 设置中断优先级分组2
    delay_init();             //延时函数初始化
    uart_init(115200);        //串口初始化为9600
    exfuns_init();        //为fatfs相关变量申请内存

    LED_Init();         //LED初始化

    mem_init();            //初始化内存池


    while (SD_Initialize())                    //检测SD卡
    {

        delay_ms(200);
        LED0 = !LED0;//DS0闪烁
    }
    exfuns_init();                            //为fatfs相关变量申请内存
    f_mount(fs[0], "0:", 1);                    //挂载SD卡
    f_mount(fs[1], "1:", 1);                    //挂载FLASH.
    while (exf_getfree("0", &total, &free))    //得到SD卡的总容量和剩余容量
    {
        delay_ms(200);
        LED0 = !LED0;//DS0闪烁
    }
    //打印大小
    printf("SD卡容量:%d MB\r\nSD卡剩余容量:%d MB\r\n", total / 1024, free / 1024);

    //write_to_txt("text.txt", str);    // 写入字符串到txt文件
    //append_to_file("text.txt", str1);    // 写入字符串到txt文件
    process_lines_from_txt("text.txt");


    while (1) {
        t++;
        delay_ms(200);
        LED0 = !LED0;
    }
}

支持的文件列表：

 //文件类型列表
const u8 *FILE_TYPE_TBL[6][13]=
{
{"BIN"},			//BIN文件
{"LRC"},			//LRC文件
{"NES"},			//NES文件
{"TXT","C","H"},	//文本文件
{"MP1","MP2","MP3","MP4","M4A","3GP","3G2","OGG","ACC","WMA","WAV","MID","FLAC"},//音乐文件
{"BMP","JPG","JPEG","GIF"},//图片文件

下图是读取到的数据展示：