使用数组读取和写入文本文件

Question

I am working on a program in the C language for a class and I am stuck. I have been researching everywhere (textbooks, Internet, classmates, class notes) and I can't seem to find the problem. Here is the following assignment:

Write a function that reads an input file and creates a sorted output file. The function prototype is void file_sort(char *infile, char *outfile). The function takes the file names as parameters. The input file contains student information and has the following format. The first line contains the number of students in the file. Each subsequent line contains information about one student. Each line contains three fields namely student ID, grade, and GPA in that order separated by blanks. The student ID is a positive integer. The grade is a character. The GPA is a double type value. The function sorts the student information in the ascending order of student ID. The ordered student information is written to the output file. The output file has the same format as the input file. The function dynamically allocates three arrays and stores the student information into the arrays. The three arrays are simultaneously sorted. The sorted array information is written to the output file. The dynamic arrays are freed when the function completes its work. Structures should not be used.

Just a couple of notes: (1) I have been programming in the Java language for approximately 3 years. Programming isn't necessarily new to me. The C language is however. (2) If I have not properly presented my question, you may certainly say so but please be considerate. After all, I still consider myself a "newbie".

Here is my current code. The first block is my calling of the function file_sort() in main. It is menu driven (1-11 options for the user. This is option 9).

else if (response == 9)
    {
        char *input_file_name;
        char *output_file_name;
        printf("Enter input file name: ");
        scanf("%s", input_file_name);
        printf("Enter output file name: ");
        scanf("%s", output_file_name);
        file_sort(input_file_name, output_file_name);
        printf("File sorted and rewritten\n");
    }

Here is the function declared outside of main.

void file_sort(char *infile, char *outfile)
{
    FILE *input;
    FILE *output;
    input = fopen(infile, "r");
    output = fopen(outfile, "w");
    int size = 100;
    int *id_array;
    id_array = (int*)malloc(size*sizeof(int));
    char *grade_array;
    grade_array = (char*)malloc(size*sizeof(char));
    double *gpa_array;
    gpa_array = (double*)malloc(size*sizeof(double));
    char grade;
    int id;
    double gpa;
    int number_students, j;
    if (input == NULL)
    {
        printf("File could not be opened\n");
    }
    fscanf(input, "%d", &number_students);
    while ((fscanf(input,"%d %c %lf", &id, &grade, &gpa)) == 3)
    {
        j = number_students;
        while((j >= 0) && (id_array[j] > id))
        {
            if (id_array[0] == 0)
            {
                id_array[0] = id;
                break;
            }
            id_array[j + 1] = id_array[j];
            j--;
        }
        if (j < 0)
        {
            j = 0;
        }
        id_array[j] = id;
        gpa_array[j] = gpa;
        grade_array[j] = grade;
    }

    int i;
    for (i = 0; i <= number_students; i++)
    {
        fprintf(output, "%d %c %lf\n", id_array[i], grade_array[i], gpa_array[i]);
    }
    free(id_array);
    free(grade_array);
    free(gpa_array);
    fclose(input);
    fclose(output);
}

If there is any information I need to include to help answer this question better, please let me know. Thank you very much.

It appears that the sorting is not working. Below I have posted the file which needs to be sorted along with the final output.

To be sorted (first number declares number of students):

5
6029 A 3.5
3920 B 2.3
9287 A 3.1
1029 C 1.7
8391 B 2.9

"Sorted" file after running:

1029 C 1.700000
8391 B 2.900000
9287 £ 0.000000
9287   0.000000
10696720 ¸ 0.000000
10696720  0.000000'

???

Answer 1

I am not sure about exact problem.

one visible issue is in else if (response == 9) section

char *input_file_name;
char *output_file_name;

are char pointers. These pointers used to get the file names. But there is no memory is allocated for this.

else if (response == 9)
    {
        char *input_file_name; <------
        char *output_file_name;
        printf("Enter input file name: "); 
        scanf("%s", input_file_name);<--------------
        printf("Enter output file name: ");
        scanf("%s", output_file_name);<--------------
        file_sort(input_file_name, output_file_name);
        printf("File sorted and rewritten\n");
    }

Either allocate dynamically or make it as char array.

char input_file_name[50];
char output_file_name[50];

Answer 2

i dont know but maybe you can do this too?

int i; for (i = 0; i <= number_students; i++, i--) {