how to read byte by byte from a file

Question

I want to read the 4 first bytes from a binnary file which is a song.wav type. In a .wav file the 4 first bytes must be 52-46-49-49 and I have to read them to check later if they are true.

The thing is that I have a compile arror at the fread line which says invalid conversion from "unsigned char" to "void" and initialzing argument 1 of 'size_t fread(void*,size_t,size_t,FILE*) and i dont know what it means.

I saw in a previous topic tha this is the way that fread must be done if i want to read byte by byte. If anyone has any idea of how i can read byte by byte and store them in an array that be great. Thank you.

void checksong(char *argv[]){
    FILE *myfile;
    int i;
    unsigned char k[4];
    myfile=fopen(argv[2],"r");
    i=0;
    for(i=0; i<4; i++){
       fread(k[i],1,1,myfile);
    }
    for(i=0; i<4; i++){
       printf("%c\n", k[i]);
    }                                  
    return ;
}

Answer 1

It is a single error:

Invalid conversion from unsigned charto void* initializing argument 1 of

size_t fread(void*,size_t,size_t,FILE*)

It means k[i] is an unsigned char, and not a pointer. You should use &k[i] or k+i.

However, you don't really need to read byte by byte. You can read 4 bytes, no loops involved:

fread(k, 4, 1, myfile);

Printing the numbers:

for (i=0; i<4; i++)
   printf("%d\n", k[i]);

Answer 2

In order to read exactly one byte and store it into k at index i, you need to provide the address of element i

for(i=0; i<4; i++){
    fread(&k[i],1,1,myfile);
}

However, you'd rather read the whole 4 bytes in one go if you're interested in them 4. So no for loop at all, and just do:

fread(k,1,4,myfile);

It is also good practice to test the return code of fread (and any I/O operation for that matter) in case it fails. man fread for more information.