Writing and Reading Formatetd Text Files

#include <stdio.h>

#define TITLE_LEN 80
#define AUTHOR_LEN 80
#define CAPACITY 100

typedef struct {
    char title[TITLE_LEN];
    char writer[AUTHOR_LEN];
} Publication;

void store_text();
void load_text();

int main() {
    store_text();
    load_text();
    return 0;
}

void store_text() {
    Publication list[] = {
        {"Sculptor", "Scott McCloud"},
        {"The Lighthouse", "Chris Ware"},
        {"Human Limitations", "Samuel Johnson"},
        {"Onward: A Life of Margaret Atwood", "Rosemary Sullivan"},
        {"Above the Earth", "Rohinton Mistry"},
        {"School Memories", "He Zhaowu"},
        {"Fate", "Cai Chongda"}
    };
    int total = sizeof(list) / sizeof(list[0]);
    FILE *file_ptr = fopen("books.txt", "w");
    if (!file_ptr) {
        printf("Unable to create text file.\n");
        return;
    }
    for (int idx = 0; idx < total; idx++)
        fprintf(file_ptr, "%-38s %-18s\n", list[idx].title, list[idx].writer);
    fclose(file_ptr);
}

void load_text() {
    Publication collection[CAPACITY];
    FILE *file_ptr = fopen("books.txt", "r");
    if (!file_ptr) {
        printf("Unable to open text file.\n");
        return;
    }
    int pos = 0, items_read;
    while (1) {
        items_read = fscanf(file_ptr, "%s%s", collection[pos].title, collection[pos].writer);
        if (items_read != 2) break;
        pos++;
    }
    for (int idx = 0; idx < pos; idx++)
        printf("%d. %-38s%-18s\n", idx + 1, collection[idx].title, collection[idx].writer);
    fclose(file_ptr);
}

Omitting the check for successful fscanf may cause an extra iteration when the file ends with whitespace, reading invalid data.

---

Block-Based Binary File I/O

#include <stdio.h>

#define TITLE_LEN 80
#define AUTHOR_LEN 80
#define CAPACITY 100

typedef struct {
    char title[TITLE_LEN];
    char writer[AUTHOR_LEN];
} Publication;

void save_binary();
void fetch_binary();

int main() {
    save_binary();
    fetch_binary();
    return 0;
}

void save_binary() {
    Publication list[] = {
        {"Sculptor", "Scott McCloud"},
        {"The Lighthouse", "Chris Ware"},
        {"Human Limitations", "Samuel Johnson"},
        {"Onward: A Life of Margaret Atwood", "Rosemary Sullivan"},
        {"Above the Earth", "Rohinton Mistry"},
        {"School Memories", "He Zhaowu"},
        {"Fate", "Cai Chongda"}
    };
    int total = sizeof(list) / sizeof(list[0]);
    FILE *file_ptr = fopen("books.dat", "wb");
    if (!file_ptr) {
        printf("Unable to create binary file.\n");
        return;
    }
    fwrite(list, sizeof(Publication), total, file_ptr);
    fclose(file_ptr);
}

void fetch_binary() {
    Publication collection[CAPACITY];
    FILE *file_ptr = fopen("books.dat", "rb");
    if (!file_ptr) {
        printf("Unable to open binary file.\n");
        return;
    }
    int pos = 0, items_read;
    while (1) {
        items_read = fread(&collection[pos], sizeof(Publication), 1, file_ptr);
        if (items_read != 1) break;
        pos++;
    }
    for (int idx = 0; idx < pos; idx++)
        printf("%d. %-38s%-18s\n", idx + 1, collection[idx].title, collection[idx].writer);
    fclose(file_ptr);
}

Without verifying fread results, trailing file markers can produce spurious records.

---

String and Character Based Text Processing

#include <stdio.h>
#define COUNT 5
#define BUFFER 80

void save_strings();
void load_strings();
void load_chars();

int main() {
    save_strings();
    load_strings();
    load_chars();
    return 0;
}

void save_strings() {
    const char *lyrics[COUNT] = {
        "Working's Blues",
        "Everything Will Flow",
        "Streets of London",
        "Perfect Day",
        "Philadelphia"
    };
    FILE *file_ptr = fopen("songs.txt", "w");
    if (!file_ptr) {
        printf("Cannot open file for writing.\n");
        return;
    }
    for (int i = 0; i < COUNT; i++) {
        fputs(lyrics[i], file_ptr);
        fputc('\n', file_ptr);
    }
    fclose(file_ptr);
}

void load_strings() {
    char buffer[COUNT][BUFFER];
    FILE *file_ptr = fopen("songs.txt", "r");
    if (!file_ptr) {
        printf("Cannot open file for string reading.\n");
        return;
    }
    for (int i = 0; i < COUNT; i++)
        fgets(buffer[i], BUFFER, file_ptr);
    for (int i = 0; i < COUNT; i++)
        printf("%d. %s", i + 1, buffer[i]);
    fclose(file_ptr);
}

void load_chars() {
    FILE *file_ptr = fopen("songs.txt", "r");
    if (!file_ptr) {
        printf("Cannot open file for char reading.\n");
        return;
    }
    int ch;
    while ((ch = fgetc(file_ptr)) != EOF)
        putchar(ch);
    fclose(file_ptr);
}

Escape sequences like \' represent a single quote; the backslash does not appear literally in output.

---

Counting Lines and Non-Whitespace Characters

#include <stdio.h>
#include <ctype.h>

int main() {
    FILE *file_ptr = fopen("input.txt", "r");
    if (!file_ptr) {
        perror("Open error");
        return 1;
    }
    int line_count = 0, letter_count = 0;
    int cur;
    while ((cur = fgetc(file_ptr)) != EOF) {
        if (cur == '\n') line_count++;
        if (!isspace(cur)) letter_count++;
    }
    if (letter_count > 0) line_count++;
    fclose(file_ptr);
    printf("Lines: %d\nNon-whitespace chars: %d\n", line_count, letter_count);
    return 0;
}

---

Processing Structured Records from File

#include <stdio.h>
#include <string.h>
#define SIZE 10

typedef struct {
    long roll;
    char full_name[20];
    float part_a;
    float part_b;
    float total;
    char status[10];
} Candidate;

void input(Candidate arr[], int lim);
void print_all(Candidate arr[], int lim);
void export_pass(Candidate arr[], int lim);
int evaluate(Candidate arr[], int lim, Candidate passed[]);

int main() {
    Candidate group[SIZE], cleared[SIZE];
    int num_passed;
    double rate;
    input(group, SIZE);
    num_passed = evaluate(group, SIZE, cleared);
    printf("\nAll candidates:\n");
    print_all(group, SIZE);
    export_pass(group, SIZE);
    rate = (double)num_passed / SIZE * 100;
    printf("Pass rate: %.2f%%\n", rate);
    return 0;
}

void print_all(Candidate arr[], int lim) {
    printf("RollNo\tName\tPartA\tPartB\tTotal\tStatus\n");
    for (int i = 0; i < lim; i++)
        printf("%ld\t%s\t%.2f\t%.2f\t%.2f\t%s\n",
               arr[i].roll, arr[i].full_name, arr[i].part_a, arr[i].part_b,
               arr[i].total, arr[i].status);
}

void input(Candidate arr[], int lim) {
    FILE *src = fopen("candidates.txt", "r");
    if (!src) {
        printf("Failed to open source file.\n");
        return;
    }
    for (int i = 0; i < lim; i++)
        fscanf(src, "%ld %s %f %f", &arr[i].roll, arr[i].full_name, &arr[i].part_a, &arr[i].part_b);
    fclose(src);
}

void export_pass(Candidate arr[], int lim) {
    FILE *dest = fopen("passed_list.txt", "w");
    if (!dest) {
        printf("Failed to create output file.\n");
        return;
    }
    fprintf(dest, "RollNo\tName\tPartA\tPartB\tTotal\tStatus\n");
    for (int i = 0; i < lim; i++) {
        if (strcmp(arr[i].status, "Pass") == 0)
            fprintf(dest, "%ld\t%s\t%.2f\t%.2f\t%.2f\t%s\n",
                    arr[i].roll, arr[i].full_name, arr[i].part_a, arr[i].part_b,
                    arr[i].total, arr[i].status);
    }
    fclose(dest);
}

int evaluate(Candidate arr[], int lim, Candidate passed[]) {
    int count = 0;
    for (int i = 0; i < lim; i++) {
        arr[i].total = arr[i].part_a + arr[i].part_b;
        if (arr[i].total >= 60) {
            strcpy(arr[i].status, "Pass");
            passed[count++] = arr[i];
        } else strcpy(arr[i].status, "Fail");
    }
    return count;
}

---

Random Selection of Students and Saving Results

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define NUM_STUDENTS 80
#define PICK_COUNT 5

typedef struct {
    int roll;
    char full_name[20];
    char section[20];
} Pupil;

int main() {
    Pupil roster[NUM_STUDENTS];
    int chosen[PICK_COUNT];
    FILE *src = fopen("roster.txt", "r");
    if (!src) {
        printf("Cannot access roster file.\n");
        return 1;
    }
    for (int i = 0; i < NUM_STUDENTS; i++)
        fscanf(src, "%d %s %s", &roster[i].roll, roster[i].full_name, roster[i].section);
    fclose(src);
    srand((unsigned)time(NULL));
    for (int i = 0; i < PICK_COUNT; i++) {
        int idx;
        do idx = rand() % NUM_STUDENTS;
        while (roster[idx].roll == -1);
        chosen[i] = idx;
        roster[idx].roll = -1;
    }
    printf("Selected pupils:\n");
    for (int i = 0; i < PICK_COUNT; i++) {
        int idx = chosen[i];
        printf("Roll: %d, Name: %s, Section: %s\n",
               roster[idx].roll, roster[idx].full_name, roster[idx].section);
    }
    char out_name[50];
    printf("Enter output file name: ");
    scanf("%s", out_name);
    FILE *dest = fopen(out_name, "w");
    if (!dest) {
        printf("Cannot open destination file.\n");
        return 1;
    }
    fprintf(dest, "Selected pupils:\n");
    for (int i = 0; i < PICK_COUNT; i++) {
        int idx = chosen[i];
        fprintf(dest, "Roll: %d, Name: %s, Section: %s\n",
                roster[idx].roll, roster[idx].full_name, roster[idx].section);
    }
    fclose(dest);
    return 0;
}