script/tool to convert file to C/C++ source code array

On Debian and other Linux distros is installed by default (along with vim) the xxd tool, which, given the -i option, can do what you want:

matteo@teodeb:~/Desktop$ echo Hello World\! > temp
matteo@teodeb:~/Desktop$ xxd -i temp 
unsigned char temp[] = {
  0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x21,
  0x0a
};
unsigned int temp_len = 13;

One simple tool can be found here:

#include <stdio.h>
#include <assert.h>

int main(int argc, char** argv) {
    assert(argc == 2);
    char* fn = argv[1];
    FILE* f = fopen(fn, "rb");
    printf("char a[] = {\n");
    unsigned long n = 0;
    while(!feof(f)) {
        unsigned char c;
        if(fread(&c, 1, 1, f) == 0) break;
        printf("0x%.2X,", (int)c);
        ++n;
        if(n % 10 == 0) printf("\n");
    }
    fclose(f);
    printf("};\n");
}

The accepted answer using xxd tool is nice if you are on a *nix-like system. Here is a "one-liner" for any system that has python executable on the path:

python -c "import sys;a=sys.argv;open(a[2],'wb').write(('const unsigned char '+a[3]+'[] = {'+','.join([hex(b) for b in open(a[1],'rb').read()])+'};').encode('utf-8'))" <binary file> <header file> <array name>

< binary file > is the name of the file you want to turn into a C header, < header file > is the name of the header file, and < array name > is the name you want the array to have.

The above one-line Python command does approximately the same as the following (much more readable) Python program:

import sys

with open(sys.argv[2],'wb') as result_file:
  result_file.write(b'const char %s[] = {' % sys.argv[3].encode('utf-8'))
  for b in open(sys.argv[1], 'rb').read():
    result_file.write(b'0x%02X,' % b)
  result_file.write(b'};')