fwrite in C giving different values in output files

Question

why are the output files different when I use fwrite in another function VERSUS fwrite in the same function?

output1.txt contains garbage value like Ê, which is NOT corr

Answer 1

In function writeData change

fwrite(&buf, sizeof(char), strlen(buf), fp1);

to

fwrite(buf, sizeof(char), strlen(buf), fp1);

Answer 2

In the writeData function, in your call to fwrite:

fwrite(&buf, sizeof(char), strlen(buf), fp1);

the variable buf is a pointer to the first character in the string to write. It's of typechar *. However the expression &buf is a pointer to the variable buf, its type is char **. It's not the same data.

---

It works if buf is an array because both then buf (which is really &buf[0]) and &buf points to the same location. They are still different types though.

For example with

char buf[2];

then buf decays to a pointer to the arrays first element (i.e. &buf[0]) and is of type char *. The expression &buf is a pointer to the array and is of type char (*)[2].

Somewhat graphically

+--------+--------+
| buf[0] | buf[1] |
+--------+--------+
^
|
&buf[0]
|
&buf

Two pointers to the same location, but different types and different semantic meanings.

Answer 3

writeData() should call fwrite(buf, ...) not fwrite(&buf, ...)