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PO
 

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    <p>Here's the one I'm using:</p> <pre><code>#include &lt;stdint.h&gt; #include &lt;stdlib.h&gt; static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'}; static char *decoding_table = NULL; static int mod_table[] = {0, 2, 1}; char *base64_encode(const unsigned char *data, size_t input_length, size_t *output_length) { *output_length = 4 * ((input_length + 2) / 3); char *encoded_data = malloc(*output_length); if (encoded_data == NULL) return NULL; for (int i = 0, j = 0; i &lt; input_length;) { uint32_t octet_a = i &lt; input_length ? (unsigned char)data[i++] : 0; uint32_t octet_b = i &lt; input_length ? (unsigned char)data[i++] : 0; uint32_t octet_c = i &lt; input_length ? (unsigned char)data[i++] : 0; uint32_t triple = (octet_a &lt;&lt; 0x10) + (octet_b &lt;&lt; 0x08) + octet_c; encoded_data[j++] = encoding_table[(triple &gt;&gt; 3 * 6) &amp; 0x3F]; encoded_data[j++] = encoding_table[(triple &gt;&gt; 2 * 6) &amp; 0x3F]; encoded_data[j++] = encoding_table[(triple &gt;&gt; 1 * 6) &amp; 0x3F]; encoded_data[j++] = encoding_table[(triple &gt;&gt; 0 * 6) &amp; 0x3F]; } for (int i = 0; i &lt; mod_table[input_length % 3]; i++) encoded_data[*output_length - 1 - i] = '='; return encoded_data; } unsigned char *base64_decode(const char *data, size_t input_length, size_t *output_length) { if (decoding_table == NULL) build_decoding_table(); if (input_length % 4 != 0) return NULL; *output_length = input_length / 4 * 3; if (data[input_length - 1] == '=') (*output_length)--; if (data[input_length - 2] == '=') (*output_length)--; unsigned char *decoded_data = malloc(*output_length); if (decoded_data == NULL) return NULL; for (int i = 0, j = 0; i &lt; input_length;) { uint32_t sextet_a = data[i] == '=' ? 0 &amp; i++ : decoding_table[data[i++]]; uint32_t sextet_b = data[i] == '=' ? 0 &amp; i++ : decoding_table[data[i++]]; uint32_t sextet_c = data[i] == '=' ? 0 &amp; i++ : decoding_table[data[i++]]; uint32_t sextet_d = data[i] == '=' ? 0 &amp; i++ : decoding_table[data[i++]]; uint32_t triple = (sextet_a &lt;&lt; 3 * 6) + (sextet_b &lt;&lt; 2 * 6) + (sextet_c &lt;&lt; 1 * 6) + (sextet_d &lt;&lt; 0 * 6); if (j &lt; *output_length) decoded_data[j++] = (triple &gt;&gt; 2 * 8) &amp; 0xFF; if (j &lt; *output_length) decoded_data[j++] = (triple &gt;&gt; 1 * 8) &amp; 0xFF; if (j &lt; *output_length) decoded_data[j++] = (triple &gt;&gt; 0 * 8) &amp; 0xFF; } return decoded_data; } void build_decoding_table() { decoding_table = malloc(256); for (int i = 0; i &lt; 64; i++) decoding_table[(unsigned char) encoding_table[i]] = i; } void base64_cleanup() { free(decoding_table); } </code></pre> <p>Keep in mind that this doesn't do any error-checking while decoding - non base 64 encoded data will get processed.</p>
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    1. POHow do I base64 encode (decode) in C?
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    1. USuser2859193
    1. USryyst
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    1. COIt doesn't make any sense to use this if there is a library.
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      1. USDiego Woitasen
    2. COYou can skip the libm and math.h "dependency" as well the need for floating point operations (which are slow on some hardware), by using `*output_length = ((input_length - 1) / 3) * 4 + 4;` in the beginning of base64_encode.
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      1. USFabian Henze
    3. COI realize it is "no error checking", but especially notice that although the decoding table in the decoder is an array of 256, since char is signed on most architectures, you are really indexing from -128 to 127. Any character with the high bit set will cause you to read outside the allocated memory. Forcing the data lookup to be an unsigned char clears that up. You still get garbage out for garbage in, but you won't segfault.
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      1. USbitmusher
 

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