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10 years, 10 months ago.

Retrieve File from SD Card

I am using SDFilesystem library for the FRDM-KL46Z to write some data to the SD card as various files with filenames as 1,2,3 so on . How can I retrieve the files or the content so that I can do some string operations over it and then send it over SPI ?

How exactly can I retrieve Data from the SD Card?

2 Answers

Robert Spilleboudt
10 years, 10 months ago.

The information in the Handbook is very short because you can use the C library . Look at http://www.cplusplus.com/reference/cstdio/ . Hope this help you to start.

Paul Staron
10 years, 10 months ago.

Here are some snips from a program I have to read temperature logs from a SD card. This can give you an idea how to start. Each record on the file is separated by ","

This code will not run, there is a lot more behind it. But shows how I extract the data from the SD card which is in the same format.

SD read

#include "mbed.h"


// This part code reads back time and scale data for each data file 

char *pEnd,*p;
fp = fopen("/sd/logs.txt", "r");
    if(fp == NULL) {SDmenu();}      
    fgets (buf, 128, fp);
    p = strtok (buf,",");log1time = atoi(p);
    p = strtok (NULL, ",");log1scale = atoi(p);
    p = strtok (NULL, ",");log2time = atoi(p);
    p = strtok (NULL, ",");log2scale = atoi(p);
    p = strtok (NULL, ",");log3time = atoi(p);
    p = strtok (NULL, ",");log3scale = atoi(p);
    p = strtok (NULL, ",");log4time = atoi(p);
    p = strtok (NULL, ",");log4scale = atoi(p);
    p = strtok (NULL, ",");log5time = atoi(p);
    p = strtok (NULL, ",");log5scale = atoi(p);
    p = strtok (NULL, ",");log6time = atoi(p);
    p = strtok (NULL, ",");log6scale = atoi(p);
    p = strtok (NULL, ",");log7time = atoi(p);
    p = strtok (NULL, ",");log7scale = atoi(p);
    p = strtok (NULL, ",");log8time = atoi(p);
    p = strtok (NULL, ",");log8scale = atoi(p);    
    fclose (fp);

// This part code reads from a file until it reaches the end.
char *pEnd,*p;
FILE *fp = fopen("/sd/log1data.txt", "r");
while(fgets (buf, 27, fp) != NULL){
        
        temp = strtof (buf, &pEnd);
        char* logtime = strtok (buf,",");
        logtime = strtok (NULL,",");        
                    
        plottemp = 180 - (temp*4);       
        if(xt==0) {xt=plottemp;}
        oled.drawLine (x,plottemp,x,xt,oled.toRGB(255, 0, 0));          
        xt=plottemp; x++;
        oled.setFontSize(FONT12X16);oled.setFontColor(oled.toRGB(255,255,255));   
        oled.locate (0,0);oled.printf("  %s",logtime); 
       
    }
 fclose (fp);

// This complete code below gives me all my files and memory used and capacity.


void SDfiles(){
    oled.setFontColor(oled.toRGB(0,255,128));oled.setFontSize(FONT8X12);
    float capacity=sd.disk_sectors()*512;
    oled.locate (5,2);oled.printf("%2.3f Gb Capacity ", capacity/1000000000);
    oled.locate (0,4);oled.setFontColor(oled.toRGB(255,255,255));                 
                DIR *d = opendir("/sd");               // Opens the root directory of the local file system
                struct dirent *p;
                    while((p = readdir(d)) != NULL) {         // Print the names of the files in the local file system
                        oled.printf(" %s\n", p->d_name);              // to stdout.
                    }
                closedir(d);
    FILE *fp = fopen("/sd/logs.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp);fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log1data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log2data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log3data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log4data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log5data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log6data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log7data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/log8data.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/maxmin.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/Templogger.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/Templogtime.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    fp = fopen("/sd/system.txt", "r");fseek(fp, 0, SEEK_END);filesize = ftell(fp)+filesize;fseek(fp, 0, SEEK_SET);fclose(fp);
    
    oled.setFontSize(FONT8X12);oled.setFontColor(oled.toRGB(0,255,128)); 
    oled.locate (2,18);oled.printf("%3.2f Kb used  ",filesize/1000);
    oled.printf("%d Stored logs",logs);
    
}

// This resets the SD card with the files I am using

void SDreset()
{
    FILE *fp = fopen("/sd/logs.txt", "w");fclose(fp);
    fp = fopen("/sd/log1data.txt", "w");fclose(fp);
    fp = fopen("/sd/log2data.txt", "w");fclose(fp);
    fp = fopen("/sd/log3data.txt", "w");fclose(fp);
    fp = fopen("/sd/log4data.txt", "w");fclose(fp);
    fp = fopen("/sd/log5data.txt", "w");fclose(fp);
    fp = fopen("/sd/log6data.txt", "w");fclose(fp);
    fp = fopen("/sd/log7data.txt", "w");fclose(fp);
    fp = fopen("/sd/log8data.txt", "w");fclose(fp);
    fp = fopen("/sd/maxmin.txt", "w");fclose(fp);
    fp = fopen("/sd/Templogger.txt", "w");fclose(fp);
    fp = fopen("/sd/Templogtime.txt", "w");fclose(fp);
    fp = fopen("/sd/system.txt", "w");fclose(fp);         
    }