File content as of revision 8:edb685e9d93e:

#include "mbed.h"
#include <math.h>
#include <cstring>
#include <stdlib.h>
#include "SDFileSystem.h"

Serial pc(PA_9, PA_10);
//Serial serial(PA_2, PA_3);

char fileName[64];
char buff[1024];

FILE * fp_open;

// mosi, miso, sclk, cs, name
SDFileSystem sd(PB_15, PB_14, PB_13, PB_12, "sd");

void getFileName ()
{
    pc.printf("type in a file name:\r\n");
    pc.scanf("%s", fileName);
    pc.printf("got file name:%s\r\n", fileName);
}

void readFile(char * name)
{
    fp_open = fopen(name, "r");
    pc.printf("reading\r\n");
    for (int i = 0; fscanf(fp_open, "(%s)", buff) == 1; i++) 
    {
        pc.printf("(%s)\r\n", buff);
    }
    pc.printf("read done.\r\n");
}

void writeFile(char * name)
{
    int a = 0,
        b = 0,
        c = 0;
    fp_open = fopen(name, "w");
    pc.printf("writing\r\n");
    pc.printf("type in data(use '0 0 0' to end)\r\n");
    while(1)
    {
        pc.scanf("%d %d %d", &a, &b, &c);
        if (a == 0 && b == 0 && c == 0)
            break;
        else
        {
            pc.printf("writing data: (%d,%d,%d)\r\n", a, b, c);
            fprintf(fp_open, "(%d,%d,%d)", a, b, c);
        }
    }
    fclose(fp_open);
    pc.printf("write done.\r\n");
}

int main ()
{
    pc.baud(115200);
    pc.printf("hello\r\n");
    getFileName();
    writeFile(fileName);
    readFile(fileName);
}