"#include" a text file in a C program as a char[]

Question

I'd suggest using (unix util)xxd for this. you can use it like so

$ echo hello world > a
$ xxd -i a

outputs:

unsigned char a[] = {
  0x68, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x0a
};
unsigned int a_len = 12;

The question was about C but in case someone tries to do it with C++11 then it can be done with only little changes to the included text file thanks to the new raw string literals:

In C++ do this:

const char *s =
#include "test.txt"
;

In the text file do this:

R"(Line 1
Line 2
Line 3
Line 4
Line 5
Line 6)"

So there must only be a prefix at the top of the file and a suffix at the end of it. Between it you can do what you want, no special escaping is necessary as long as you don't need the character sequence )". But even this can work if you specify your own custom delimiter:

R"=====(Line 1
Line 2
Line 3
Now you can use "( and )" in the text file, too.
Line 5
Line 6)====="

I like kayahr's answer. If you don't want to touch the input files however, and if you are using CMake, you can add the delimeter character sequences on the file. The following CMake code, for instance, copies the input files and wraps their content accordingly:

function(make_includable input_file output_file)
    file(READ ${input_file} content)
    set(delim "for_c++_include")
    set(content "R\"${delim}(\n${content})${delim}\"")
    file(WRITE ${output_file} "${content}")
endfunction(make_includable)

# Use like
make_includable(external/shaders/cool.frag generated/cool.frag)

Then include in c++ like this:

constexpr char *test =
#include "generated/cool.frag"
;

You have two possibilities:

1. Make use of compiler/linker extensions to convert a file into a binary file, with proper symbols pointing to the begin and end of the binary data. See this answer: Include binary file with GNU ld linker script.
2. Convert your file into a sequence of character constants that can initialize an array. Note you can't just do "" and span multiple lines. You would need a line continuation character (\), escape " characters and others to make that work. Easier to just write a little program to convert the bytes into a sequence like '\xFF', '\xAB', ...., '\0' (or use the unix tool xxd described by another answer, if you have it available!):

Code:

#include <stdio.h>

int main() {
    int c;
    while((c = fgetc(stdin)) != EOF) {
        printf("'\\x%X',", (unsigned)c);
    }
    printf("'\\0'"); // put terminating zero
}

(not tested). Then do:

char my_file[] = {
#include "data.h"
};

Where data.h is generated by

cat file.bin | ./bin2c > data.h

ok, inspired by Daemin's post i tested the following simple example :

a.data:

"this is test\n file\n"

test.c:

int main(void)
{
    char *test = 
#include "a.data"
    ;
    return 0;
}

gcc -E test.c output:

# 1 "test.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.c"

int main(void)
{
    char *test =
# 1 "a.data" 1
"this is test\n file\n"
# 6 "test.c" 2
    ;
    return 0;
}

So it's working but require data surrounded with quotation marks.

You can do this using objcopy:

objcopy --input binary --output elf64-x86-64 myfile.txt myfile.o

Now you have an object file you can link into your executable which contains symbols for the beginning, end, and size of the content from myfile.txt.