how to read csv file ?

This is a discussion on how to read csv file ? within the C Programming forums, part of the General Programming Boards category; hi all.. i'm creating program that will read a csv file.. let say,,the csv file content 10 rows of data ...

  1. #1
    Registered User
    Join Date
    Jun 2003
    Posts
    5

    how to read csv file ?

    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..
    ??

  2. #2
    Code Goddess Prelude's Avatar
    Join Date
    Sep 2001
    Posts
    9,796
    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.
    My best code is written with the delete key.

  3. #3
    .
    Join Date
    Nov 2003
    Posts
    307
    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.

  4. #4
    Registered User
    Join Date
    Jun 2003
    Posts
    5
    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

  5. #5
    Just Lurking Dave_Sinkula's Avatar
    Join Date
    Oct 2002
    Posts
    5,006
    >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 
    */
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  6. #6
    Code Goddess Prelude's Avatar
    Join Date
    Sep 2001
    Posts
    9,796
    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';
      }
    }
    My best code is written with the delete key.

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