C fprintf hexadecimal incorrect output

Question

I have a char array composed of hex values that looks similar to this:

 char str[] =
        "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
        "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
        "\x80\xe8\xdc\xff\xff\xff";

After manipulating this string, I want to fprintf this string to a file using this statement:

fprintf(fp, "%X\n", str);

but I'm getting an output similar to this:

65C58A20

Seems like it got condensed to a single hex number. How can I fprintf the str in the same form I declared it above, with separate hex values for each individual byte?

Might sprintf() work? Use it to convert the char array to a string, then print out that string to file instead? — verbose
– verbose, Commented Jan 24, 2017 at 0:37
@TheEyesHaveIt: See my updated answer. I'm assuming you want to print the same textual representation that was part of your source code back out as a string (as opposed to writing the actual bytes that are described by your source code). — Kerrek SB
– Kerrek SB, Commented Jan 24, 2017 at 0:45
Suggest editing "\x80\xe8\xdc\xff\xff\xff --> "\x80\xe8\xdc\xff\xff\xff"; (add last 2 characters, if that is what you meant. — chux
– chux, Commented Jan 24, 2017 at 0:53

Kerrek SB · Accepted Answer · 2017-01-24 00:44:16Z

2

What you need is this:

for (size_t i = 0; i != sizeof str - 1; ++i)
    fprintf(fp, "\\x%02x", (unsigned char)str[i]);

edited Jan 24, 2017 at 0:44

answered Jan 24, 2017 at 0:38

Kerrek SB

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