解析 C 中的制表符分隔文本文件

Question

so, i saw an older post that showed how to do this, but for some reason it seems it no longer works, my input file consists of a header row, and then 15 rows of input, each with 5 columns, first 2 are strings, the last 3 are ints, i have a struct to store them, and im trying to write the contents into an array of these structs

FName LName Credits Transactions Modifer
John Doe    83000   2   1
Jane Doe    64000   5   3

I tried

    struct customer cust = { NULL,NULL,0,0,0};
    char line[SIZE] = { 0 }, * ptr = NULL;
    cust.fName = malloc(15);
    cust.lName = malloc(15);
    printf("%d\n", &fp);
    if (NULL == (fp = fopen("../customers.txt", "r")))
    {
        perror("Error while opening the file.\n");
        exit(EXIT_FAILURE);
    }
    while (EOF != fscanf(fp, "%s", line))
    {
        ptr = strtok(line, "\\");
        cust.fName = ptr;
        printf("%s", ptr);
        while (EOF != (ptr = strtok(NULL, "\\")))
        {
            i++;
            printf("%s",ptr);
            if (i == 1)
                cust.lName = ptr;
            else if (i == 2)
                cust.miles = atoi(ptr);
            else if (i == 3)
                cust.years = atoi(ptr);
            else if (i == 4)
                cust.sequence = atoi(ptr);
        }

        i = 0;
        printf("After Reading: fName:[%s] lName:[%s] miles:[%d] years:[%d]\n", cust.fName, cust.lName, cust.miles, cust.years);
    }

For some reason, the printf within the inner while loop only prints "(null)" , and errors out when i==2 with the error

File: minkernel\crts\ucrt\inc\corecrt_internal_strtox.h
Line: 1772

Expression: _p != nullptr

I dont have any idea what that error message means, so i dont know what im doing wrong

Answer 1

Also, Craig, do you mind giving an example, im pretty new to using C and am unfamiliar with fgets

Okay. Because your code was a bit far off, I had to refactor it heavily.

Your code was only handling a single customer record. What you need to do is a separate struct instance for each line (ie customer). So, we want to use realloc to enlarge a dynamic array of our struct customer .

And, you have allocate memory [on the heap] for each string in a record (ie first and last names). So, we have to use strdup

Anyway, here's the code:

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

struct customer {
    char *fName;
    char *lName;
    int miles;
    int years;
    int sequence;
};

int
main(void)
{
    FILE *fp;
    char buf[1000];
    char *cp;
    char *bp;
    struct customer *list = NULL;
    int custcnt = 0;
    struct customer *cust;
    const char *delim = "\t\n";
    int field;

    fp = fopen("customers.txt","r");
    if (fp == NULL) {
        perror("error opening file");
        exit(1);
    }

    while (1) {
        cp = fgets(buf,sizeof(buf),fp);
        if (cp == NULL)
            break;

        // increase size of customer list/array by one
        list = realloc(list,sizeof(*list) * (custcnt + 1));
        if (list == NULL) {
            perror("malloc");
            exit(1);
        }

        // point to place for next customer
        cust = &list[custcnt];

        // advance customer count
        ++custcnt;

        // preclear the new record in case of a line that is malformed (i.e.
        // missing some data)
        memset(cust,0,sizeof(*cust));

        // loop through and store all customer record fields
        bp = buf;
        for (field = 0;  field < 5;  ++field) {
            cp = strtok(bp,delim);
            if (cp == NULL)
                break;
            bp = NULL;

            switch (field) {
            case 0:
                cust->fName = strdup(cp);
                break;

            case 1:
                cust->lName = strdup(cp);
                break;

            case 2:
                cust->miles = atoi(cp);
                break;

            case 3:
                cust->years = atoi(cp);
                break;

            case 4:
                cust->sequence = atoi(cp);
                break;
            }
        }

        printf("After Reading: fName:[%s] lName:[%s] miles:[%d] years:[%d]\n",
            cust->fName, cust->lName, cust->miles, cust->years);
    }

    fclose(fp);

    return 0;
}