如何读取文本文件中的逗号分隔行并将其字段插入到结构指针数组中？

Question

I've been trying to figure this one out for a while now, and I feel like I have to be close. Basically, I have a data file containing various country records separated by new lines. Each record contains comma separated fields, of which I am trying to extract certain ones.

For example (as a single line):

60,AFG,Afghanistan,Asia,Southern and Central Asia,652090,1919,22720000,45.9,5976,Afganistan/Afqanestan,Islamic Emirate,Mohammad Omar,1,AF

Each one of these lines will make up a struct. Essentially, I want to read each one of these lines and insert it into an array of struct pointers (so dynamically). I also only want specific fields. When I "tokenize" the line I want the fields for code, name, population, and life expec. respectively:

AFG, Afghanistan, 22720000, 45.

My thought was to use fgets() to read each line in the file, and in a loop malloc() some memory for the pointers, tokenize on the fields I want, then insert. However, something that I'm doing must be wrong, as various tests don't seem to show anything in my output.

Here is my work thus far. I would appreciate any and all help.

#include "allheaders.h" // contains all common headers for personal use

#define BUF_SIZE 512
#define NUM_RECS 238

typedef struct {
   char code[4];
   char name[40];
   int population;
   float lifeExpectancy;
} Country;

typedef Country *countryPtr;

int main( int argc, const char* argv[] ) {

/* Opening the file */
FILE *filePtr;  // pointer to file
if ((filePtr = fopen("AllCountries.dat", "r")) == NULL) {   // if couldn't open file
    printf("Error opening file\n"); // error message
    exit(1);
}

/* Reading the file */
char buffer[BUF_SIZE];  // buffer to read
int index = 0;
char *token;
countryPtr *myCountries = malloc(sizeof(*myCountries) * NUM_RECS);
for(int i = 0; i < NUM_RECS; ++i) {
    myCountries[i] = malloc(sizeof(*myCountries[i]));
}

while (fgets(buffer, BUF_SIZE, filePtr) != NULL) {

    token = strtok(buffer,",");
    token = strtok(NULL, ",");
    strcpy(myCountries[index]->code, token);
    token = strtok(NULL, ",");
    strcpy(myCountries[index]->name, token);
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    myCountries[index]->population = atoi(token);
    token = strtok(NULL, ",");
    myCountries[index]->lifeExpectancy = atof(token);
    //printf("%s", buffer);
    index++;
}

printf("%s", myCountries[1]->code); // test?
free(myCountries);

}

Answer 1

Have a look at the following. In the first instance you will need to do some work to improve the areas marked NYI

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

#define BUF_SIZE 512
#define NUM_RECS 238

typedef struct {
  char code[4]; // NYI - magic numbers
  char name[41]; // NYI - magic numbers
  int population; // NYI - what if atoi fails? 
  float lifeExpectancy; // NYI - what if atof fails?
} Country;

typedef Country* countryPtr;

int main( int argc, const char* argv[] ) {
  /* Opening the file */
  FILE *filePtr;  // pointer to file
  if ((filePtr = fopen("a.txt", "r")) == NULL) {   // if couldn't open file
    printf("Error opening file\n"); // error message
    exit(1);
  }

  /* Reading the file */
  char buffer[BUF_SIZE];  // buffer to read
  int index=0;
  char *token; // NYI - initial value
  countryPtr* myCountries = calloc(NUM_RECS, sizeof(countryPtr));
  for(int i = 0; i < NUM_RECS; ++i) {
    myCountries[i] = calloc(1, sizeof(Country));
  }

  while (fgets(buffer, BUF_SIZE, filePtr) != NULL) {
    // NYI - magic lengths / overflow strcpy targets

    token = strtok(buffer,","); // NYI - This is probably not the best way to do this. At least fold into a loop.
    token = strtok(NULL, ",");
    strcpy(myCountries[index]->code, token);
    token = strtok(NULL, ",");
    strcpy(myCountries[index]->name, token);
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");
    token = strtok(NULL, ",");

    myCountries[index]->population = atoi(token); // NYI - atoi failure
    token = strtok(NULL, ",");
    myCountries[index]->lifeExpectancy = atof(token); // NYI - atof failure
    printf("%s", buffer);
    index++;
  }

  printf("%s\n", myCountries[0]->code); // test? NYI - need more proof
  free(myCountries); // NYI - this is a sequence - need to free each of the new elements 
}

Answer 2

I took a different approach to solving it based on your code and data file. I tested it. It works with a file of the record type you showed. Hopefully it will explain some things and make your work easier and give you a good place to work from.

I don't like to write programs in a way that has to pre-count (time consuming) or pre-know the number of records in a file on general principles except maybe in rare cases. So when reading files I prefer to allocate memory as I go. Now if there's a big file and a lot of data, then you have to come up with a better memory management scheme than to keep it all in memory. At some point you're better off going with a canned db solution of some sort. MySQL, an API, library, parser, etc... but this should work for small files.

Usually in C on UNIX, exit(0) means success, exit(-1) means failure. Also since your country codes were 3 characters, the field to hold it has to be at least 4 characters for the trailing '\\0'

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

#define MAXRECL   512
#define MAXFIELDS 100
#define MAXFIELDL 80

// Field indicies

#define COUNTRY_CODE    1
#define COUNTRY_NAME    2
#define POPULATION      7
#define LIFE_EXPECTANCY 8

#define CCMAX           3
#define CNMAX           40

typedef struct Country {
   struct Country *next;
   char  code[CCMAX + 1];  // (Need room for trailing '\0')
   char  name[CNMAX + 1];  // (Need room for trailing '\0')
   int   population;
   float lifeExpectancy;
} country_t;

country_t *countryRecords;

int main( int argc, const char* argv[] ) {

    FILE *fp;
    if ((fp = fopen("AllCountries.dat", "r")) == NULL) {  
        printf("Error opening file\n"); 
        exit(-1);
    }
    int totalCountries = 0;
    char buf[MAXRECL];
    char fields[MAXFIELDS][MAXFIELDL];
    country_t *prev_country = NULL;
    while (fgets(buf, MAXRECL, fp) != NULL) {
        ++totalCountries;      
        country_t *country = calloc(sizeof(struct Country), 1);
        if (country == NULL) {
            fprintf(stderr, "Out of memory\n");
            exit(-1);
        }
        char *field = strtok(buf, ",");
        int i = 0;
        while(field != NULL) {
          strncpy(fields[i++], field, MAXFIELDL);
          field = strtok(NULL, ",");
        }        
        strcpy(country->code, fields[COUNTRY_CODE]);
        strcpy(country->name, fields[COUNTRY_NAME]);
        country->population = atoi(fields[POPULATION]);
        country->lifeExpectancy = atof(fields[LIFE_EXPECTANCY]);

        if (countryRecords == NULL)
            countryRecords = country;
        else 
            prev_country->next = country;
        prev_country = country;  
    }
    printf("Total countries: %d\n", totalCountries);

    country_t *country = countryRecords;
    while(country != NULL) {
        printf("%3s %30s  Population: %7d Life Expectancy: %5.2f\n",
            country->code, country->name, country->population, country->lifeExpectancy); 
        country_t *prev_country = country;
        country = country->next;
        free(prev_country);
    }
    printf("Done\n");
    exit(0);
}