In C: Format for printing YYYYMMDD as MM-DD-YYYY

Question

Say I want to print using

printf(format, "YYYYMMDD");

How would format look if I wanted my output to look like "MM-DD-YYYY"?

Thanks.

Let me add my full code so there's no confusion.

I have a sruct defined as

typedef struct{
       char     *dt;    
       float     op, hi, lo, cl, vl; 
}STOCKDATA; 

Then call a function:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>

#include "../include/struct.h"
#include "../include/function.h"
#include "../include/utility.h"

#define linemax 514 
void  stockData(char *ticker)     
{
     extern STOCKDATA *stockdata;
     extern int nrows;

     //count number of lines in file..............................
       char *filename;
       mkstring("../data/", ticker, filename);
       nrows=linesInFile(filename);

     //allocate stockdata.........................................

       stockdata=malloc_stockdata(0,nrows-1);

     //open file to read into stockdata...........................
     FILE *fp;
     fp = fopen(filename, "r");   
     if(fp==NULL) 
     {
         printf("%s%s\n", "Can't open data file ", filename);
         exit(1);
     }

     char delimiters[] = " ,";
     char line[linemax];

     char *tmp;

     fgets(line, linemax, fp);               //skip header 

     int  count=0;                           //count number of lines
     while( fgets(line, linemax, fp) !=NULL)
     {
          tmp=strtok(line, delimiters);      //ticker (skipped)

          stockdata[count].dt= strtok(NULL, delimiters);         //date
//printf("%s\n", stockdata[count].dt);
          stockdata[count].op=atof(strtok(NULL, delimiters));   //open
          stockdata[count].hi=atof(strtok(NULL, delimiters));   //high
          stockdata[count].lo=atof(strtok(NULL, delimiters));   //low
          stockdata[count].cl=atof(strtok(NULL, delimiters));   //close
          stockdata[count].vl=atof(strtok(NULL, delimiters));   //volume

          count++;
     }

     fclose(fp);
}

Then call the function:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#include "../include/struct.h"
#include "../include/function.h"
#include "../include/utility.h"


#define cutoff 10
void writeData(char *ticker)
{

   extern STOCKDATA  *stockdata;
   extern int nrows;

  //open output file........................................
   char *filename;
   mkstring("../output/", ticker, filename);

    FILE *fp;
    fp = fopen(filename, "w");
    if(fp==NULL)
    {
         printf("%s%s\n", "Can't open data file ", filename);
         exit(1);
    }


  int k;
  char *format="%-15s%-10.2f%-10.2f%-10.2f%-10.2f%-10.0f\n";
  for (k=nrows-cutoff; k<nrows; k++)
  {
   fprintf(fp, format, stockdata[k].dt,
                       stockdata[k].op,
                       stockdata[k].hi,
                       stockdata[k].lo,
                       stockdata[k].cl,
                       stockdata[k].vl );

  }

  fclose(fp);

}

Now, where I define 'format' in the last function call, I'm trying to make it print stockdata[k].dt in a MM-DD-YYYY format. The string in the data file is in YYYYMMDD.

Answer 1

What is the format of your source data?

If it's really a string "YYYYMMDD", just use %.4s and %.2s with the appropriate offsets added to the pointer to get at the parts you want.

If it's a number of the form YYYYMMDD (decimal), use x/10000, x/10%100, and x%100 to get at the parts, and %.4d and %.2d for the formats.

If it's an actual time, use strftime.

Answer 2

You want to look into strptime and strftime. First, you need to parse the date you have (using strptime) like so:

struct tm timeStruct;
strptime(dateString, "%Y%m%d", &timeStruct);

Then convert it to the new format using strftime:

strftime(outputString, sizeof(outputString), "%m-%d-%Y", &timeStruct);

Now outputString contains the date in the format you want.

Answer 3

You might be looking for strptime and strftime.