Merged files versus appending files in C - c

Question

Can someone please help explain the difference in C and how my file fails to merge, and appends instead? The background is I am on an online computer science class this summer which uses C language, all we are given is read the entire texbook (732 pages), and do 20 projects over the course of 8 weeks, with no actual instruction, lecture, slides, or explanations. Please explain it so I can learn as I need to actually understand these terms to be better and progress in my Electrical Engineering program. I have contacted my professor for help but the answers are always short and uninformative, and you guys have provided so much more quality feedback to date. Also I do get that he is right and it was appended and not merged, but any feedback how i could of rectified this will help as well. Thank you again!
#include <stdio.h>
#include <stdlib.h>
FILE *inptr1, *inptr2, *outptr;
int main()
{
char c;
char file1[30], file2[30], file3[30];
printf("Enter the first files name\n");
gets(file1);
printf("Enter the second files name\n");
gets(file2);
printf("Enter the file name that will store the data from the other two files\n");
gets(file3);
inptr1 = fopen("C:\\Users\\Eric\\Desktop\\file1.txt","r");
inptr2 = fopen("C:\\Users\\Eric\\Desktop\\file2.txt","r");
if( inptr1 == NULL || inptr2 == NULL )
{
perror("Error ");
printf("Press any key to exit!\n");
exit(1);
}
outptr = fopen("C:\\Users\\Eric\\Desktop\\file3.txt","w");
if( outptr == NULL )
{
perror("Error ");
printf("Press any key to exit!\n");
exit(1);
}
while( ( c = fgetc(inptr1) ) != EOF )
fputc(c,outptr);
while( ( c = fgetc(inptr2) ) != EOF )
fputc(c,outptr);
printf("The two files were sucessfully merged into %s \n",file3);
fclose(inptr1);
fclose(inptr2);
fclose(outptr);
return 0;
}
Page 611 #5 Write a complete C program. Use the two files provided. Your program should not assume that you know which file is shorter.
5) Write a function to merge two sorted files of names and write the names to a
new file.
Was the only direction I was given as far as to what the program was supposed to do.
and this was the feedback i received, "Did you look at the resulting file?The girls names are all at the bottom. You were to merge the files,not append the files."
Thank you again in advance for your valuable feedback as it has taught me so much to date.

Answer 1

You're going to need to look at the contents of each file and write them to the third file in sorted order. That seems to be what the assignment is asking you to do. What you're doing currently is dumping the contents of file1.txt into file3.txt followed by the contents of file2.txt. You want to end up with a sorted list containing the contents of both files.

Answer 2

There are many ways to accomplish your requirements. This is just one that jumps out:
Steps to perform:
1 Open two existing files (fopen(fp, "r");), and one new file (fopen(fp, "w");)
2 write all lines of first file, then the second file to the third file. (fopen(), fgets(), fputs(), fclose(), etc.)
3 Read third file into an array of strings, keeping a count of the total number of strings read. close file.
4 Sort array of strings. (qsort())
5 Open third file, Write sorted array of strings into that file.
6 Close all files, free all memory.
Note, using this method, it does not matter if the two original files are sorted, or not, (Assignment says they are, but does not matter). The qsort routine will completely sort the string array either way.
qsort()
Most of the functions referenced are straight forward to use. qsort() is a little weird.
Here is an example showing how to set up qsort() for use sorting an array of strings:
For an array of strings: strings with the number of strings being say: cnt then:
qsort(strings, cnt, sizeof(char*), sortstring);
//With the function sortstring defined as:
static int sortstring( const void *str1, const void *str2 )
{
const char *rec1 = *(const char**)str1;
const char *rec2 = *(const char**)str2;
int val = strcmp(rec1, rec2);
return val;
}
string arrays
Creating an array of strings can also be challenging. Again, there are several ways to do this, here are two:
If you know the dimensions of each line, and the total number of lines in both files, then you can do it like this:
char strArray[numLines][longestLine];
If you don't, then you have to determine that at run-time by getting a count of the total number of lines, say when you are reading them from each file. And you will also need the length of the longest line found in both files, say by using strlen() on each one at some point as it is read or written. Once you have that information, you can create your string array like this:
char **strings=0;
Then, before you need it, create memory for it:
char **allocMemoryStr(char **strings, int numStrings, int maxLen)
{
int i;
strings = calloc(sizeof(char*)*(numStrings+1), sizeof(char*));
for(i=0;i<numStrings; i++)
{
strings[i] = calloc(sizeof(char)*maxLen + 1, sizeof(char));
}
return strings;
}
Finally, when you are finished using dynamically allocated memory, you must always free it:
void freeMemoryStr(char **strings, int numStrings)
{
int i;
for(i=0;i<numStrings; i++)
if(strings[i]) free(strings[i]);
free(strings);
}