CODEWITHSUNDEEP
cbinaryfilesfread
TenG
TenG

Reputation: 4004

fread binary file truncates data

I have a file that was created by an application on the same PC as my code. This has the following at the start:

$ od -c save.data
0000000  \0  \0  \0 006  \0  \0  \0      \0   D  \0   V  \0   E  \0   1
.
.

Using the following code in C to read the file in:

FILE *encfile;
char inba[8192];  // input file is < 500 bytes so this is plenty big enough

memset(inba, 0, sizeof(inba));
encfile = fopen(argv[1], "rb");
int br = fread(inba, 1, 8192, encfile);
printf ("Bytes read: %d\n", br);

The above prints Bytes read: 409 correctly.

The issue is that the inba variable is 'empty', because I think the first byte read is 0, which gets treated as end of string. There are a number of 0 value bytes in the file.

How can I get C to see this as a 409 byte array?

The data will get passed to other functions that expect this as a char * variable.

Is this an endianess issue?

Upvotes: 0

Views: 167

Answers (1)

MikeCAT
MikeCAT

Reputation: 75062

Binary data is generally not strings. Keep track the size by yourself.

This code will dump the contents of the array in hexadecimal:

// br and inba are the variable in OP's code

for (int i = 0; i < br; i++) {
    printf("%02X", (unsigned char)inba[i]);
    if (i + 1 >= br || i % 16 == 15) putchar('\n'); else putchar(' ');
}

Upvotes: 3

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