how to read csv file ?

**kosong** · 11-12-2003

hi all..

i'm creating program that will read a csv file..
let say,,the csv file content 10 rows of data like this..

Code:

10,23,444,-33,45,33,22,445,44,34
1,23,444,-33,45,33,22,445,44,34
-120,23,444,-33,45,33,22,445,44,34
10,23,44,-33,45,33,22,445,4,34
10,23,4,-33,45,33,22,445,44,34
10,23,-44,-33,145,33,22,4,44,34
10,23,444,-33,45,33,22,445,44,34
10,23,444,-33,45,233,22,445,44,34
10,23,444,-33,45,33,22,-45,44,34
10,23,444,-33,45,323,22,445,44,34

now, algorithm that i'm using is,
1) read the data line by line using fgets() and save it to
a char array , let say

szLine_data[256]

2) then seperate and throw out comma

3) the problem now is,, i'm doing processing character by character.
so,, after throw out comma, i dont know how to put let say character 4, 4, 4 to a char array..

what i'm doing now is,,

Code:

while(szLine_data[l] != ',')
{
  szTmp[l] = szLine_data[l];
  l++;
}

it means that szTmp content comma also at the last element..
how to throw the comma and the balance of the element..
??

**Prelude** · 11-12-2003

CSV is a convoluted design, it's not as simple as just looking for commas if you're using real CSV files:

Code:

int csv_parse ( char *line, char *list[], int size )
{
  char *p;
  char *dp;
  int inquote;
  int na;
  char prevc = ',';

  dp = NULL;
  inquote = 0;
  na = 0;
  prevc = ',';
  for ( p = line; *p != '\0'; prevc = *p, p++ ) {
    if ( prevc == ',' && !inquote ) {
      if ( dp != NULL )
        *dp = '\0';
      if ( na >= size )
        return na;
      list[na++] = p;
      dp = p;
      if ( *p == '"' ) {
        inquote = 1;
        continue;
      }
    }
    if ( inquote && *p == '"' ) {
      if ( p[1] != '"' )
        inquote = 0;
      p++;
    }
    if ( *p != ',' || inquote )
      *dp++ = *p;
  }
  if ( dp != NULL )
    *dp = '\0';
  if ( na < size )
    list[na] = NULL;

  return na;
}

Of course, if you don't worry about the quoting rules, you can shorten the code considerably.

**jim mcnamara** · 11-12-2003

See the thread - Simple Question - by Amazing Rando

I posted an 4 line algorithm (no quotes) for decomposing
a known line of csv data into a struct. The length of the algorithm is unaffected by the number of fields, but does have a set-up algorithm that executes once - which IS affected by the number of fields.

Prelude is right, full-blown CSV is a lot harder to parse.

**kosong** · 11-13-2003

thank you for your reply...

I still dont understand your code.. to difficult for me...
i dont understand why we need NULL....

so,, i shorterned your code...

Code:

 while(!feof(ptrDat_file))
    {
      fgets(szLine_dat,LINE_SIZE,ptrDat_file);
      nSize = strlen(szLine_dat);

      nReturn = csv_parse( szLine_dat, nSize );

      printf("%s\n", szTmp_data);       

    }  
  return 0;
}

  
int csv_parse ( char *line, int size )
{
  char *p;
  char *dp;
  int inquote;
  int na;
  int nTo_comma;
  char prevc = ',';
  char *list[256];

  dp = NULL;
  // inquote = 0;
  na = 0;
  prevc = ',';

  nTo_comma=0;
  for ( p = line; *p != '\n'; p++ ) 
    {   
      nTo_comma++;
      list[nTo_comma] = p;
      if(*p == prevc)
	{
	  printf("%s\t", list);
	
	  return na;
	}

    }
  
  printf("\n");

  return na;
}

in while{} looping,,
i get a line of data from csv file and pass to csv_parse() function..

in csv_parse() function,, what i hope is,,,
it should print the 1st data in that line with comma..
ex:

Code:

10,23,444,-33,45,33,22,445,44,34

will print

Code:

10,

am I wrong??

if i can do this, after i can up my code 1 step,, to print every data separated by comma..

thank you for your kind help

**Dave_Sinkula** · 11-13-2003

>while(!feof(ptrDat_file))
Why it's bad to use feof() to control a loop

Just a thought...

Code:

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

#define ARRAYSIZE(x)  (sizeof(x)/sizeof(*(x)))

int main(void)
{
   const char filename[] = "file.csv";
   /*
    * Open the file.
    */
   FILE *file = fopen(filename, "r");
   if ( file )
   {
      int array[10][10];
      size_t i, j, k;
      char buffer[BUFSIZ], *ptr;
      /*
       * Read each line from the file.
       */
      for ( i = 0; fgets(buffer, sizeof buffer, file); ++i )
      {
         /*
          * Parse the comma-separated values from each line into 'array'.
          */
         for ( j = 0, ptr = buffer; j < ARRAYSIZE(*array); ++j, ++ptr )
         {
            array[i][j] = (int)strtol(ptr, &ptr, 10);
         }
      }
      fclose(file);
      /*
       * Print the data in 'array'.
       */
      for ( j = 0; j < i; ++j )
      {
         printf("array[%lu]: ", (long unsigned)j);
         for ( k = 0; k < ARRAYSIZE(*array); ++k )
         {
            printf("%4d ", array[j][k]);
         }
         putchar('\n');
      }
   }
   else /* fopen() returned NULL */
   {
      perror(filename);
   }
   return 0;
}

/* my output
array[0]:   10   23  444  -33   45   33   22  445   44   34 
array[1]:    1   23  444  -33   45   33   22  445   44   34 
array[2]: -120   23  444  -33   45   33   22  445   44   34 
array[3]:   10   23   44  -33   45   33   22  445    4   34 
array[4]:   10   23    4  -33   45   33   22  445   44   34 
array[5]:   10   23  -44  -33  145   33   22    4   44   34 
array[6]:   10   23  444  -33   45   33   22  445   44   34 
array[7]:   10   23  444  -33   45  233   22  445   44   34 
array[8]:   10   23  444  -33   45   33   22  -45   44   34 
array[9]:   10   23  444  -33   45  323   22  445   44   34 
*/

**Prelude** · 11-13-2003

Maybe this will be more to your liking:

Code:

#include <stdio.h>

size_t comma_parse ( char *line, char *list[], size_t size );

int main ( void )
{
  char   *p = "10,23,444,-33,45,33,22,445,44,34";
  char   *list[11];
  size_t n;
  size_t i;

  n = comma_parse ( p, list, sizeof list );
  for ( i = 0; i < n; i++ )
    puts ( list[i] );
  
  return 0;
}

size_t comma_parse ( char *line, char *list[], size_t size )
{
  char   *p;
  size_t n;

  p = line;
  n = 0;
  for ( ; ; ) {
    /* Ditch leading commas */
    while ( *p == ',' )
      p++;
    /* Nothing of use */
    if ( *p == '\0' )
      return n;
    /* Save the string */
    list[n++] = p;
    /* Find the next field */
    while ( *p != ',' && *p != '\0' )
      p++;
    /* Nothing else of use or too many fields */
    if ( *p == '\0' || n >= size )
      return n;
    /* Split the field */
    *p++ = '\0';
  }
}

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