C Programming: Reading data from a file, dynamically allocating memory, placing contents in struct array

You are reusing structArray as both the base of the array and a pointer to the current element. This won't work. We need two variables.

There are a number of "loose" variables related to the dynamic array. It's cleaner to define a struct (e.g. dynarr_t below) to contain them and pass just the struct pointer around.

When you're duplicating the string, you must allocate strlen + 1 [not just strlen]. But, the entire function does what strdup already does.

I tried to save as much as possible, but I've had to refactor the code a fair bit to incorporate all the necessary changes.

By passing sizeof(*structArray) to the arrnew function, this allows the struct to be used for arbitrary size array elements.

Anyway, here's the code:

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

#define sysfault(_fmt...) \
    do { \
        printf(_fmt); \
        exit(1); \
    } while (0)

#define EXIT_CODE_FAIL 1
#define ROW_COUNT 10
#define BUFFER_SIZE 255
#define VALID_ARG_COUNT 2

struct Student {
    float gpa;
    char *name;
};

// general dynamic array control
typedef struct {
    void *base;                         // base address
    size_t size;                        // bytes in array element
    size_t count;                       // current number of used entries
    size_t max;                         // maximum number of entries
    size_t grow;                        // number of entries to grow
} dynarr_t;

// arrfind -- return pointer to array element
void *
arrfind(dynarr_t *arr,size_t idx)
{
    void *ptr;

    ptr = arr->base;
    idx *= arr->size;
    ptr += idx;

    return ptr;
}

// arrnew -- create new array control
dynarr_t *
arrnew(size_t siz,size_t grow)
// siz -- sizeof of array element
// grow -- number of elements to grow
{
    dynarr_t *arr;

    arr = calloc(1,sizeof(*arr));
    if (arr == NULL)
        sysfault("arrnew: calloc fail -- %s\n",strerror(errno));

    arr->size = siz;
    arr->grow = grow;

    return arr;
}

// arrgrow -- grow array [if necessary]
// RETURNS: pointer to element to fill
void *
arrgrow(dynarr_t *arr)
{
    void *ptr;

    // grow array if necessary
    // NOTE: use of a separate "max" from "count" reduces the number of realloc
    // calls
    if (arr->count >= arr->max) {
        arr->max += arr->grow;
        arr->base = realloc(arr->base,arr->size * arr->max);
        if (arr->base == NULL)
            sysfault("arrgrow: realloc failure -- %s\n",strerror(errno));
    }

    // point to current element
    ptr = arrfind(arr,arr->count);

    // advance count of elements
    ++arr->count;

    return ptr;
}

// arrtrim -- trim array to actual number of elements used
void
arrtrim(dynarr_t *arr)
{

    arr->base = realloc(arr->base,arr->size * arr->count);
    if (arr->base == NULL)
        sysfault("arrtrim: realloc failure -- %s\n",strerror(errno));

    arr->max = arr->count;
}

void
validateMalloc(void *ptr)
{

    if (ptr == NULL) {
        perror("validateMalloc");
        exit(1);
    }
}

void
validateOpenFile(FILE *ptr)
{

    if (ptr == NULL) {
        perror("validateOpenFile");
        exit(1);
    }
}

// resize string from initial data buffer
char *
trimStringFromBuffer(char *dataBuffer)
{

#if 0
#if 0
    char *string = calloc(1,strlen(dataBuffer));
#else
    char *string = calloc(1,strlen(dataBuffer) + 1);
#endif
    validateMalloc(string);
    strcpy(string, dataBuffer);
#else
    char *string = strdup(dataBuffer);
    validateMalloc(string);
#endif

    return string;
}

// read the file, pack contents into struct array
dynarr_t *
readFileContents(char *filename)
{
    dynarr_t *arr;

    // setup for loop
    float currentStudentGpa = 0;
    char studentNameBuffer[BUFFER_SIZE];
    struct Student *structArray;

    arr = arrnew(sizeof(*structArray),10);

    FILE *pFile = fopen(filename, "r");
    validateOpenFile(pFile);

    // loop through, get contents, of eaach line, place them in struct
    while (fscanf(pFile, "%s\t%f", studentNameBuffer, &currentStudentGpa) > 0) {
        structArray = arrgrow(arr);
        structArray->name = trimStringFromBuffer(studentNameBuffer);
        structArray->gpa = currentStudentGpa;
    }

    fclose(pFile);

    arrtrim(arr);

    return arr;
}