如何把純文字檔放到 C 執行檔中？

請見 Embedding a File in an Executable 及 Convert a File to a C Data Structure

一般方法至少三大類，最常見的就是利用 fopen 之類的 API 來自行處理 file I/O, 一種是第一篇文章說的，把 text file 轉成 object file 後再來引用指標的方式操作，一種是第二篇文章講的，將 text file 轉成 c char array struct。

先來看看文字檔，我改成多行：

$ cat data.txt
Hello, Wade.
This is a test line here
And this is the last line.
Add 4th line here.

底下是執行畫面，是在 cygwin 下執行的，因為 objcopy 的參數不太一樣，請修改成適當的，值得注意的是用 objdump 來看轉換後的 object file 內部的 symbol name 為 _binary_data_txt_start

$ objcopy.exe -I binary -O elf32-i386 -B i386 data.txt data.o

$ objdump.exe -x data.o

data.o:     file format elf32-i386
data.o
architecture: i386, flags 0x00000010:
HAS_SYMS
start address 0x00000000

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .data         00000054  00000000  00000000  00000034  2**0
                  CONTENTS, ALLOC, LOAD, DATA
SYMBOL TABLE:
00000000 l    d  .data  00000000 .data
00000000 g       .data  00000000 _binary_data_txt_start
00000054 g       .data  00000000 _binary_data_txt_end
00000054 g       *ABS*  00000000 _binary_data_txt_size

底下列出測試用的 hello.c 及編譯、執行畫面，值得注意的是，因為 gcc 會在 extern symbol 前加上底線，因此命名方式跟原文不太一樣。

$ cat hello.c
#include 

extern char binary_data_txt_start;
extern char binary_data_txt_end;

main()
{
    char*  p = &binary_data_txt_start;

    while ( p != &binary_data_txt_end ) putchar(*p++);
}


$ gcc hello.c data.o

$ ./a
Hello, Wade.
This is a test line here
And this is the last line.
Add 4th line here.

第二種方式的 script 內容及執行畫面如下：

$ cat 2c.sh
#!/bin/bash

if [[ $# -ne 1 ]]; then
    echo "Usage: $0 FILENAME"
    exit 1
fi
file=$1

if [[ ! -f "$file" ]]; then
    echo "File not found: $file"
    exit 1
fi

cname=$file
cname=${cname//-/_}
cname=${cname//./_}

echo "static unsigned char $cname[] = {"
hexdump -v -e '" " 16/1 "  0x%02x, " "\n"' $file | \
   sed -e '$s/0x  ,//g'
echo "};"

$ ./2c.sh data.txt
static unsigned char data_txt[] = {
   0x48,   0x65,   0x6c,   0x6c,   0x6f,   0x2c,   0x20,   0x57,   0x61,   0x64, 
   0x65,   0x2e,   0x0a,   0x54,   0x68,   0x69,
   0x73,   0x20,   0x69,   0x73,   0x20,   0x61,   0x20,   0x74,   0x65,   0x73,
   0x74,   0x20,   0x6c,   0x69,   0x6e,   0x65,
   0x20,   0x68,   0x65,   0x72,   0x65,   0x0a,   0x41,   0x6e,   0x64,   0x20,
   0x74,   0x68,   0x69,   0x73,   0x20,   0x69,
   0x73,   0x20,   0x74,   0x68,   0x65,   0x20,   0x6c,   0x61,   0x73,   0x74,
   0x20,   0x6c,   0x69,   0x6e,   0x65,   0x2e,
   0x0a,   0x41,   0x64,   0x64,   0x20,   0x34,   0x74,   0x68,   0x20,   0x6c,
   0x69,   0x6e,   0x65,   0x20,   0x68,   0x65,
   0x72,   0x65,   0x2e,   0x0a,
};