Find and replace tab in array with whitespace? - c

Question

The purpose of this exercise is to create a program that can read the contents of a file and copy it to a new one. But there is also another thing to do that I do not know how to do:
I should also replace all tabs ('\t') that i find in files with 7 white space.
How can I solve this latter problem? Thank you.
I tried it with these lines of code, but obviously not working. It also also shows the following warning:
warning C4047: '=': 'char' differs in levels of indirection from 'char [8]'
for (int i = 0; i < x; i++){
if (buf[i] == '\t') {
buf[i] = " ";
}
}
This is my code: (of course if it can be improved in some way, do not hesitate to tell me. Thank you)
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char buf[500];
FILE *fp, *nuovo;
errno_t err, err1;
/*lettura e creazione file*/
if (err = fopen_s(&fp, "text.txt", "r")) {
printf("Errore");
} else {
printf("File Letto");
}
if (err1 = fopen_s(&nuovo, "nuovo.txt", "w")) {
printf("Errore");
} else {
printf("File Creato");
}
int x = fread_s(buf, sizeof(buf), 1, 500, fp);
/*THIS IS THE PLACE FOR THE MISSING CODE*/
fwrite(&buf, 1, x, nuovo);
fclose(fp);
fclose(nuovo);
}

Answer 1

You cannot replace one character with a string, which has many characters.
One approach to solving this problem is as follows: instead of making the replacement in place, you could do it while performing the output.
Loop through the characters in buf, and check if buf[i] is a TAB. If it is not a TAB, call fputc(buf[i], nuovo). Otherwise, call fputs(" ", nuovo).

Answer 2

You have to create a new dynamic allocate buffer wher you copy all characters from your source and substitute tab by spaces:
#include <malloc.h>
const char *whitespace = " ";
int whitespaceLen = strlen( whitespace );
int newBufSize = 0;
char *newBuf = NULL;
int newBufPos = 0;
for (int i = 0; i < x; i++)
{
int isTab = buf[i] == '\t'; // test if next char in buf is tab
int charSize = isTab ? whitespaceLen : 1; // size which is neede for next char in newBuf
if ( newBufPos + charSize < newBufSize ) // test if newBuf is large enough
{
newBufSize += 500;
char *temp = realloc( newBuf, newBufSize ); // enlarge newBuf
if ( temp == NULL )
{
free( newBuf ); // out of memory, free newBuf an terminate
newBuf = NULL;
break;
}
newBuf = temp;
}
if ( isTab )
{
memcpy( newBuf+newBufPos, whitespace, whitespaceLen ); // copy whitespace blanks to newBuf
newBufPos += whitespaceLen ;
}
else
newBuf[ newBufPos++ ] = buf[i]; // copy char to newBuf
}
Note somewhere you have to free( newBuf );