Reading a CSV file in C using fgets and strtok only reads first column

Question

I have a .csv file that looks like

Config,Prob,MAN,ATL,CVERT,TVERT,LVERT,PELV,SAC,RIB,SCAP,PHUM,DHUM,PRAD,DRAD,CARP,PMC,DMC,PHX,PFEM,DFEM,PTIB,DTIB,TARS,PMT,DMT
LH,1,2,2,7,13,6,2,1,13,2,2,2,1,1,6,2,2,24,2,2,2,2,8,2,2
LH,1,0,0,0,0,0,0,0,9,1,2,2,2,2,12,2,2,18,1,1,1,1,4,1,1
LH,1,2,2,7,3,0,2,1,3,1,1,1,1,1,6,1,1,6,0,0,0,0,0,0,0
LH,1,0,0,0,13,6,2,1,8,0,2,2,1,1,0,0,0,0,0,0,0,0,0,0,0
LH,1,2,2,4,13,6,2,1,18,2,2,2,0,0,0,0,0,0,0,0,0,0,0,0,0
LH,1,0,0,0,13,6,2,1,18,2,2,2,0,0,0,0,0,0,2,2,0,0,0,0,0
LH,3,0,0,0,0,0,0,0,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
LH,1,0,0,0,13,6,2,1,24,2,2,2,2,2,12,2,2,24,2,2,2,2,8,2,2
LH,1,0,0,1,13,3,2,1,15,2,0,0,2,2,0,0,0,6,2,2,2,2,0,0,0
LH,1,0,0,0,0,0,0,0,10,0,1,1,0,0,0,0,0,18,0,0,0,0,0,0,0
LH,1,0,2,7,3,0,0,0,7,2,2,2,2,2,12,2,2,24,2,2,2,2,8,2,2
LH,1,0,0,2,0,0,0,0,14,1,2,2,2,2,0,0,0,18,2,2,2,2,0,0,0
LK,1,0,0,0,0,0,0,0,13,0,0,0,1,1,6,0,0,0,0,0,0,0,0,0,0
LK,1,2,2,7,13,6,2,1,17,1,0,0,0,0,0,0,0,6,1,1,1,1,4,1,1
LK,1,0,0,0,10,6,0,0,23,1,1,1,1,1,6,1,1,18,2,2,2,2,8,2,2
LK,1,2,2,7,0,0,0,0,18,2,0,0,1,1,12,2,2,24,2,2,2,2,8,2,2
LK,1,0,0,3,0,0,0,0,8,0,0,0,2,2,12,2,2,24,2,2,2,2,8,2,2
LK,1,2,2,7,0,0,0,0,8,0,0,0,2,2,12,2,2,24,0,0,2,2,8,2,2
LK,3,2,2,7,13,6,2,1,22,2,2,2,2,2,12,2,2,24,2,2,2,2,8,2,2
LK,1,2,2,7,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
LK,1,2,2,6,0,3,0,0,11,0,2,2,0,0,12,2,2,18,0,0,0,0,8,2,2
LK,1,2,2,7,13,6,2,1,16,2,1,1,2,2,12,2,2,6,2,2,2,2,8,2,2
LK,1,2,0,0,10,6,2,1,19,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
LK,1,2,2,5,13,6,2,1,12,1,0,0,0,0,12,2,2,6,0,0,0,0,8,2,2

I would like to ignore the text and just grab the numbers. Here is my code:

    int arr[rows][columns]; /* rows/columns of .csv file */
    char buf[1000];
    int r = 0;

    while (fgets(buf,1000,ifp)) {
        char read = 'N';
        const char *tok;
        int ret =0;
        int c = 0;
        int count = 0;
        char *ptr;
        printf("%s \n", buf);

        for (tok = strtok(buf, ","); tok && *tok; tok = strtok(NULL, ",\n")){
                printf("%s ", buf); /* replace buf with tok */
                if(isNumber(tok)==1){
                    read = 'Y';
                    ret = strtol(tok,&ptr,10);
                    arr[r][c] = ret;
                    c++;
                    printf("Entered ");
                    //printf("%ld ", arr[r][c]);
                }
                if(strtok(NULL,"\n") && read == 'N')
                    count++;
        }
        r++;
        //r -= count;
    }

isNumber is essentially an extension of isdigt and works as intended. However, whenever printing out tok for each iteration, it stops after the first comma. Sample output: Config LH LH LH LH LH LH LH LH LH LH LH LH LK LK LK LK LK LK LK LK LK LK LK LK. It seems to be reading the input just fine using fgets, as it prints out each line of the .csv file. So it seems like the issue lies with my for loop. It seems that I am incrementing my token incorrectly.

Attempting with another example:

    char alph[] = "a-b-c-e";
    for (const char *tok = strtok(alph, "-"); tok && *tok; tok = strtok(NULL, "-\0")){
        printf("%s ", tok);
    }

yields: a b c e, which is the correct result. Therefore, I feel like I am missing something here with parsing my file. Any help is appreciated. Thank you.

Jonathan Leffler · Accepted Answer · 2019-07-03T14:24:28.283

1

Your loop is:

 for (tok = strtok(buf, ","); tok && *tok; tok = strtok(NULL, ",\n")) 
 {
     …omitted…
     if (strtok(NULL, "\n") && read == 'N')
         count++;
 }

You have three calls to strtok(), and the one in the if eats up everything to the newline. I'm not sure what you were thinking there. It looks like you should omit that strtok() — but I'm not sure what you need to replace it with.

Because the second call in the loop control reads up to newline or comma (strtok(NULL, ",\n")), you can't tell when you reach the end of the line except that tok is set to NULL to indicate no more tokens.

edited Jul 03 '19 at 14:24

answered Jul 03 '19 at 14:21

Jonathan Leffler

730,956
141
904
1,278

This fixed it, thank you. I was attempting to check to see if `tok` was at the end of the line, but I got a little crazy with using `strtotk`. – hkj447 Jul 03 '19 at 14:24
1

Note that if a line came in with a single number, you'd get the newline included in the token from the `tok = strtok(buf, ",")` call to `strtok()`. Your call to `strtol()` would cheerfully ignore it, though, so there'd be no harm done. If you're not going to use the value that `strtol()` stores in `ptr`, you could pass `NULL` instead of `&ptr` and then eliminate the unused variable. Or you can validate that the number was really read — but doing that is surprisingly tricky (see [Correct usage of `strtol()`](https://stackoverflow.com/questions/14176123) for most of the sordid details). – Jonathan Leffler Jul 03 '19 at 14:31

Reading a CSV file in C using fgets and strtok only reads first column

1 Answers1