lowercase.c

/*#####################
# <lowercase.c>
#  07-29-11 John Jessie
#  <program will read from file>
#  <and print to screen one line>
#  <at a time in lowercase>
# */

#include <stdio.h> /* required for file ops */
#include <stdint.h> /* required for UINT_MAX */
#include <string.h> /* required for strncpy */
#include <ctype.h> /* required for tolower */
#include <limits.h> /* required for UINT_MAX */
#include <stdlib.h>

char *ReadFile(char *filename);

char *ReadFile(char *filename)
{
    // declare file pointer f
    FILE *f;

    f = fopen(filename, "r");
    // growable buffer for chars
    char *buffer = NULL;

    // capacity of buffer
    unsigned int capacity = 0;

    // number of chars actually in buffer
    unsigned int n = 0;

    // character read or EOF
    int c;

    // iteratively get chars from stdin
    while ( ( c = tolower(fgetc(f)) ) != EOF)
    {
        // grow buffer if necessary
        if (n + 1 > capacity)
        {
            // determine new capacity: start @32 then 2x
            if (capacity == 0)
                capacity = 32;
            else if (capacity <= (UINT_MAX / 2))
                capacity *= 2;
            else
            {
                free(buffer);
                return NULL;
            }

            // extend buffer's capacity
            char *temp = realloc(buffer, capacity * sizeof(char));
            if (temp == NULL)
            {
                free(buffer);
                return NULL;
            }
            buffer = temp;
        }

        // append current char to buffer
        buffer[n++] = c;
    }

    // return NULL if no chars received
    if (n == 0 && c == EOF)
      return NULL;

    // minimize buffer
    char *minimal = malloc((n + 1) * sizeof(char));
    strncpy(minimal, buffer, n);
    free(buffer);

    // terminate string
    minimal[n] = '\0';

    // return string
    return minimal;
}

int main(int argc, char *argv[])
{
    if ( argc < 2 )
    {
        printf("No file specified to read.");
        return 1;
    }
    char *filename = argv[1];
    printf("%s", ReadFile(filename) );
    return 0;
}