Step by Step solution about How to resolve the algorithm Stream merge step by step in the C programming language

This C code is a program that merges two sorted text files containing integer numbers into a single sorted output stream. It reads two files, specified as command-line arguments, and merges their contents in ascending order. Here's a detailed explanation:

• Header Includes and Macros:

  • The program includes necessary header files (stdio.h for input/output and stdlib.h for file handling).
  • It defines a couple of macros: GET(N) and PUT(N) are used to read and write values from/to files. These macros are used to simplify the code and avoid repetitive file operations.

• merge Function:

  • This function takes three file pointers as input: f1 for the first file, f2 for the second file, and out for the output stream.
  • Inside the function:
    • It initializes two integer variables, b1 and b2, to store the current values being read from f1 and f2, respectively.
    • It uses the GET(N) macro to read the first values from both files.
    • It enters a loop that continues as long as both f1 and f2 are not NULL (i.e., both files have values to read).
    • Inside the loop, it compares b1 and b2 and calls PUT(N) to print the smaller value to the out stream. After printing, it calls GET(N) again to read the next value from the corresponding file.
    • It handles the case where one of the files has remaining values after the loop exits by continuing to print those remaining values.

• main Function:

  • It's the program's entry point.
  • It checks if the number of command-line arguments is correct (should be 3, including the program name).
  • It calls merge with the two file names provided as arguments and the standard output stream.
  • The program returns EXIT_SUCCESS (0) to indicate successful execution.

In summary, this program merges two sorted files of integer numbers into a single sorted output stream. It does this by comparing the current values from each file and printing the smaller value first, effectively merging the two streams in ascending order.

/*
 * Rosetta Code - stream merge in C.
 * 
 * Two streams (text files) with integer numbers, C89, Visual Studio 2010.
 *
 */

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>

#define GET(N) { if(fscanf(f##N,"%d",&b##N ) != 1) f##N = NULL; }
#define PUT(N) { printf("%d\n", b##N); GET(N) }

void merge(FILE* f1, FILE* f2, FILE* out)
{
    int b1;
    int b2;

    if(f1) GET(1)
    if(f2) GET(2)

    while ( f1 && f2 )
    {
        if ( b1 <= b2 ) PUT(1)
        else            PUT(2)
    }
    while (f1 ) PUT(1)
    while (f2 ) PUT(2)
}

int main(int argc, char* argv[])
{
    if ( argc < 3 || argc > 3 )
    {
        puts("streammerge filename1 filename2");
        exit(EXIT_FAILURE);
    }
    else
        merge(fopen(argv[1],"r"),fopen(argv[2],"r"),stdout);

    return EXIT_SUCCESS;
}