Can't access my binary file after using fopen(fileName, "wb") in Xcode on Mac

Question

FILE* inFile = fopen(inF, "rb");
if (inFile == NULL) {
    printf("Invalid input!\n");
    exit(EXIT_FAILURE);
}

char* bigBuffer;
char* nextChar = (char*) malloc(sizeof(char));
unsigned long i = 0;
unsigned long j;
while ((j = fread(nextChar, sizeof(char), 1, inFile)) == 1) {
    i += j;
}
bigBuffer = malloc(i * sizeof(char));
fread(bigBuffer, sizeof(char), i, inFile);
fclose(inFile);
printf("%s\n", outF);
FILE* outFile = fopen(outF, "wb");
//if (outFile == NULL)
    //printf("null\n");
j = fwrite(bigBuffer, sizeof(char), i, outFile);
printf("%lu\n", j);
fclose(outFile);
free (bigBuffer);
free (nextChar);

I'm trying to write a binary file using fopen in wb mode. After running my program, a file of the proper name is made in the proper place, but I just can't open it or read it. When I try to open it, a message pops up saying "Can't open...." In addition, the name of the file itself isn't formatted properly in Finder (I'm on a Mac). The name is elevated and cut off a little. It definitely looks like something is wrong with the file. I tried just making a regular file using fopen in w mode, and that worked beautifully. So I'm pretty sure I'm just doing something wrong when it comes to writing binary files using wb mode. Can anyone help? Thanks.

Welcome to Stack Overflow! [Please see this discussion on why not to cast the return value of `malloc()` and family in `C`.](http://stackoverflow.com/q/605845/2173917). — Sourav Ghosh, Nov 16 '15 at 13:39
Are you sure you have fclose'd the file after fopen with wb? — V. Kravchenko, Nov 16 '15 at 13:40
Do not cast the result of `malloc` & friends in C! (Strange enough you don't even cast consistently). And format/indent your code properly! — too honest for this site, Nov 16 '15 at 13:42
Are you sure the `outF` buffer contains the correct filename ? Show the code where content of this buffer generated. — Jabberwocky, Nov 16 '15 at 14:07

score 2 · Accepted Answer · edited May 23 '17 at 11:52

2

The main problem:

you didn't seek to the beginning of the file before reading, so your call to fread to read the entire file will fail

Change:

bigBuffer = malloc(i * sizeof(char));
fread(bigBuffer, sizeof(char), i, inFile);

to:

bigBuffer = malloc(i);              // allocate buffer
rewind(inFile);                     // reset file pointer to start of file
fread(bigBuffer, 1, i, inFile);     // read entire file

Additional notes:

sizeof(char) is 1 by definition, and therefore redundant
you should not cast the result of malloc in C
you should add error checking to any call that might fail, especially I/O calls
malloc-ing a single char is inefficient - just use a local variable
reading a file one char at a time to determine its length is very inefficient

edited May 23 '17 at 11:52

Community

1
1

answered Nov 16 '15 at 13:43

Paul R

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Sir, `you have no '\0' terminator in your string when calling printf`...which one you're referring to? – Sourav Ghosh Nov 16 '15 at 13:51
1

Makes sense. However,we cannot rule out the possibility that OP wants to see if the out file name is proper or not. In that case, without seeing more code, we cannot conclude. Am I right? – Sourav Ghosh Nov 16 '15 at 13:53
1

@SouravGhosh: oh yes, maybe - it's not totally clear what the intention is, but I'll edit that stuff out for now. – Paul R Nov 16 '15 at 13:54

score 0 · Answer 2 · answered Nov 16 '15 at 13:55

0

The file with the opening in wb truncated to 0 length. Use for simultaneous read / write mode or addition mode rb +, a.

answered Nov 16 '15 at 13:55

Spouk

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18

Can't access my binary file after using fopen(fileName, "wb") in Xcode on Mac

2 Answers2