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Embed a File in a C Binary

A handy trick for embedding a file in a C or C++ binary as a byte array.

You can embed a file in a C or C++ binary as a byte array using the standard Unix utility xxd.

$ echo "test data" > data_file
$ xxd -i data_file

This prints the following to standard output:

unsigned char data_file[] = {
0x74, 0x65, 0x73, 0x74, 0x20, 0x64, 0x61, 0x74, 0x61, 0x0a
};
unsigned int data_file_len = 10;

You can write the output to a .c or .h file and include it directly in your source using an #include statement:

$ xxd -i data_file > data_file.c

If you want to access the variables from another file without including the source file directly, you'll need to use extern declarations:

extern unsigned char data_file[];
extern unsigned int data_file_len;

Note that the array produced by xxd isn't null-terminated so you can't use it directly as a C string.

Here's an alternative technique that works for embedding strings:

$ xxd -i < data_file > data_file.xxd
$ echo ', 0x00' >> data_file.xxd

Note that we're piping the input file into xxd this time instead of supplying its file name as an argument. This creates a hex-encoded byte dump without the C array wrapper. You can include it directly into a source file like this:

char data[] = {
    #include "data_file.xxd"
};