writing to a file

[boxden]

Hello, in the next piece of code I will read the content of one file and write that to another file, accept for a certrain string which I will replace by another string that the user gave as input parameter. Now my question is; in the loop while( (ptr + lengte) + i < (zin + 18)), why do you check for zin + 18 instead of zin + 19? It does not seem correct to me, but the algoritme works, so I must see something wrong. What's wrong with thinking like this"

let's say that the fgets buffer was 5 instead of 19, and the zin buffer 6.
The string you read is: abcde. The substring you want to replace is cd. The begin address of zin is 1000. The length of the substring is 2.

while(zin + i < ptr)
#
{
#
putc(*(zin + i), output);
#
i++;
#
}
#

#
fputs(argv[4], output);

this goes correctly and you write abNEWSUBSTRING but then you come in the new while and:

#
i = 0;
#

#
while( (ptr + lengte) + i < (zin + 4))

1002 (the beginaddress of the substring) + 2 < 1000 + 4. Not true so you will not write e!

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

int main (int argc, char *argv[])
{

	FILE *input;
	FILE *output;

	char *ptr;

	char zin[20];
	int lengte, i = 0;

	if (argc != 5)
	{
		printf("Aantal bestanden zijn fout\n");
		exit(0);
	}

	if ((input = fopen(argv[1], "r")) == NULL)
	{
		perror("Fout ");
		exit(0);
	}

	if ((output = fopen(argv[2], "w")) == NULL)
	{
		perror("Fout ");
		exit(0);
	}


	while (fgets(zin, 19 ,input) != NULL)
	{
		if (strstr(zin, argv[3]) == NULL)
			fputs(zin, output);
		else
		{
			lengte = strlen(argv[3]);
		
			ptr = strstr(zin, argv[3] );	
				
	
			while(zin + i < ptr)
			{
				putc(*(zin + i), output);
				i++;
			}
	
			fputs(argv[4], output);
			
			i = 0;
		
			while( (ptr + lengte) + i < (zin + 18))
			{
				putc(*(ptr + i + lengte), output);
				
				i++;
			}
		
		
		}
	}

	fclose(input);
	fclose(output);

	return 0;
}

[vart]

I do not think +18 or +19 is correct...

better get rid of the loop and just use

fputs(ptr+lengte);