从文件中读取每一行，然后在C中将该行拆分为一个字符串和一个数组

Question

Homework - I have an assignment to write a program that will read a file. The file looks like this:

B 34 55 66 456 789 78 59 2 220 366 984 132 2000 65 744 566 377 905 5000
I 9000
I 389
Dm
DM

Where B is build a binary heap from an array of numbers(the numbers following the B. I is insert a number into the array/heap Dm is delete minimum and DM is delete maximum.

I have written the code for the heap, and can fill an array with random numbers . My problem is reading that first line and parsing it into a string B and an array .

I have tried using the following code but obviously it does not work.

char line[8];
char com[1];
int array[MAX] //MAX is pre-defined as 100

FILE* fp = fopen( "input_1.txt", "r" );
if( fp )
{
    while( fgets ( line, sizeof(line), fp ) != NULL  )
    {
        sscanf(line, "%s" "%d", &com, &array );
        ... //Following this, I will have a nested if that will take
        each string and run the appropriate function.

        if ( strcmp( com, "B" ) == 0 )
        {
            fill_array( array, MAX );
            print_array( array, MAX );
        }        

I have read for about 6 hours over a total of 3 days and can't find a solution to my problem. Any help would be great.

Answer 1

Here's a little program that will open a file, read out 1 line, and split what it finds around spaces:

void main()
{
    char str[50];
    char *ptr;
    FILE * fp = fopen("hi.txt", "r");
    fgets(str, 49, fp);             // read 49 characters
    printf("%s", str);              // print what we read for fun
    ptr = strtok(str, " ");         // split our findings around the " "

    while(ptr != NULL)  // while there's more to the string
    {
        printf("%s\n", ptr);     // print what we got
        ptr = strtok(NULL, " "); // and keep splitting
    }
    fclose(fp);
 }

So were I to run this on a file containing:

B 34 55 66 456 789 78 59 2 220

I could expect to see:

B 34 55 66 456 789 78
B 
34
55 
66
456
789
78

I think you can see how to modify this to help yourself out.

Answer 2

First of all, the line array should probably have a size greater than 8, probably something like char line[256] . The same goes for the com array, which should have at least 3 characters.

char line[256];
char com[3];

You'll have to read the file line by line using fgets(line, sizeof(line), fp) and the use strtok() to separate the command from the command arguments.

char separators[] = " ";
fgets(line, sizeof(line), fp);

char * p = strtok(line, separators);    // p will be a pointer to the command string
strncpy(&com, p, sizeof(com));    // copy the command string in com


// If the command is B, read an array
if (strcmp(com, "B") == 0) {
    p = strtok(NULL, separators);

    while (p != NULL) {
        int value_to_add_to_your_array = atoi(p);
        // ... add code to add the value to your array
        p = strtok(NULL, separators);
    }

    // ... call the function that creates your heap
}

// ... add code to handle the other commands

The idea is to read the file line by line, then for each line to first read the command and based on its value determine in which way you should read the rest of the line.

In the code above I considered the B command, for which I added code to read an array.