Laboratory: Simple String Manipulation

Detecting and handling the end of file properly is often a critical issue in a file processing program. There are two options to choose from:

1. Based on the return value of fscanf: Remember that fscanf returns the number of data successfully obtained from the file - if it is less than expected, than probably the end of file has been reached.
2. Based on feof: The feof function can also be used to detect the end of a file. But there is a catch. feof returns false even after reading the last data from the file. It becomes true only after the next read attempt, that failed due to the end of file. Thus, its value has to be checked after every read attempt and the data processing needs to be stopped when it returns false.

This solution uses the return value of fscanf to detect the end of file:

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

int main() {
    FILE *fin, *fout;
    char c;

    fin = fopen("lorem.txt", "r");
    if (fin == NULL) {
        printf("Cannot open input file\n");
        return 1;
    }

    fout = fopen("output.txt", "w");
    if (fout == NULL) {
        printf("Cannot open output file\n");
        return 2;
    }

    while (fscanf(fin, "%c", &c) == 1) {
        if (islower(c))
            c = toupper(c);
        fprintf(fout, "%c", c);
    }

    fclose(fin);
    fclose(fout);

    return 0;
}

#include <stdio.h>

int main() {
    FILE *fin, *fout;
    char c;
    int line_len = 0;

    fin = fopen("lorem.txt", "r");
    if (fin == NULL) {
        printf("Cannot open input file\n");
        return 1;
    }

    fout = fopen("output.txt", "w");
    if (fout == NULL) {
        printf("Cannot open output file\n");
        return 2;
    }

    while (fscanf(fin, "%c", &c) == 1) {
        if (c == '\n') {
            line_len = 0;
        }
        else if (line_len == 20) {
            fprintf(fout, "\n");
            line_len = 0;
        }
        fprintf(fout, "%c", c);
        line_len++;
    }

    fclose(fin);
    fclose(fout);

    return 0;
}

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

typedef struct {
    int id;
    char name[101];
    char descr[201];
    int status;
} job;

int main () {
    FILE *infile, *outfile;   // file handle
    job* a;         // start address of the dynamic array    
    int N;          // number of elements in the dynamic array
    int i;          // auxiliary variable for loops
    
    // open file
    infile = fopen("jobs.txt","r");
    if (infile==NULL) {
        printf("Cannot open jobs.txt\n");
        return 1;
    }
    
    // load the content of the file into a dynamic array
    fscanf(infile, "%d", &N);   // first integer is the number of items
    a = (job*)malloc(sizeof(job)*N);
    for (i = 0; i < N; i++) {
        fscanf(infile, "%d\n", &a[i].id);
        fgets(a[i].name, 101, infile);       // we use fgets to allow space characters in the name
        a[i].name[strlen(a[i].name)-1] = '\0'; // last newline character is deleted
        fgets(a[i].descr, 201, infile);        
        a[i].descr[strlen(a[i].descr)-1] = '\0';
        fscanf(infile, "%d\n", &a[i].status);
    }
    fclose(infile);
 
    // printing jobs
    for (i = 0; i < N; i++) {
        if (strcmp(a[i].name, "Joe") == 0) {
            printf("\nJob #%d\n", a[i].id);
            printf("Description: %s\n", a[i].descr);
            printf("Status: %d\n", a[i].status);
        }
    }

    // setting the status
    for (i = 0; i < N; i++) {
        if (strcmp(a[i].name, "Joe") == 0)
            a[i].status = 1;
    }

    // saving it to file
    outfile = fopen("jobs2.txt", "w");
    if (outfile==NULL) {
        printf("Cannot open jobs2.txt\n");
        return 2;
    }    

    // save number of jobs first
    fprintf(outfile, "%d\n", N);
    // save all job assignments
    for (i = 0; i < N; i++)
        fprintf(outfile, "%d\n%s\n%s\n%d\n", a[i].id, a[i].name, a[i].descr, a[i].status);

    fclose(outfile);
    
    free(a);
    return 0;
}