README.md: add more examples

README.md

@@ -3,11 +3,22 @@
 
 This simple C library has two primary functions, **`base58check_encode`** and **`base58check_decode`**. Please refer to the auto-generated [Doxygen documentation](https://whitslack.github.io/libbase58check/base58check_8h.html) for usage details.
 
+The library comes with a command-line utility for Base58Check encoding/decoding from `stdin` to `stdout`.
+
 There are also overloaded C++ convenience functions if you are writing in C++.
 
-### Usage examples
+## Usage examples
+
+### Encoding
+Here's an example of generating a 256-bit private key and encoding it as Base58Check in Bitcoin's Wallet Import Format (WIF).
+
+#### Shell
+```bash
+$ { printf '\x80' ; head -c32 /dev/urandom ; printf '\x01' ; } | base58check
+KxmBZwPrX3u2dukBawC9u88BKAXuRRHmPwuLzLo8skAgBQoGnC6c
+```
 
-Here's an example of generating a 256-bit private key and encoding it as Base58Check in Bitcoin's Wallet Import Format (WIF):
+#### C++
 ```cpp
 #include <base58check.h>
 
@@ -27,7 +38,7 @@ int main() {
 	// wrap the key between a 0x80 type byte and a 0x01 flag byte
 	std::array<std::byte, 34> bytes;
 	bytes[0] = std::byte { 0x80 };
-	std::ranges::copy(std::as_bytes(std::span(key)), bytes.begin() + 1);
+	std::ranges::copy(as_bytes(std::span(key)), bytes.begin() + 1);
 	bytes[33] = std::byte { 0x01 };
 
 	// Base58Check encode the wrapped key and print it out
@@ -36,7 +47,60 @@ int main() {
 }
 ```
 
-And here's an example of decoding a Base58Check encoding from standard input:
+#### C
+```c
+#include <base58check.h>
+
+#include <err.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <sysexits.h>
+#include <sys/random.h>
+
+int main() {
+	struct {
+		uint8_t type;
+		uint8_t key[32];
+		uint8_t flag;
+	} buf;
+	int ret = 0;
+
+	// fill a 32-byte key using getrandom()
+	if (getrandom(buf.key, sizeof buf.key, 0) < sizeof buf.key)
+		err(EX_OSERR, "getrandom");
+
+	// wrap the key between a 0x80 type byte and a 0x01 flag byte
+	buf.type = 0x80, buf.flag = 0x01;
+
+	// Base58Check encode the wrapped key
+	char *out = NULL;
+	size_t n_out = 1; // 1 excess char for null terminator
+	if (base58check_encode(&out, &n_out, (unsigned char *) &buf, sizeof buf, 0) < 0)
+		errx(EX_UNAVAILABLE, "base58check_encode failed");
+	out[n_out] = '\0';
+
+	// print it out
+	if (puts(out) < 0 || fflush(stdout) < 0)
+		err(EX_IOERR, "stdout");
+
+	// be tidy
+	base58check_free(out);
+	return EX_OK;
+}
+```
+
+### Decoding
+And here's an example of decoding a Base58Check encoding from standard input.
+
+#### Shell
+```bash
+$ echo 1BitcoinEaterAddressDontSendf59kuE | base58check -d | hexdump -C
+00000000  00 75 9d 66 77 09 1e 97  3b 9e 9d 99 f1 9c 68 fb  |.u.fw...;.....h.|
+00000010  f4 3e 3f 05 f9                                    |.>?..|
+00000015
+```
+
+#### C++
 ```cpp
 #include <base58check.h>
 
@@ -57,12 +121,49 @@ int main() {
 	auto bytes = base58check::decode(str);
 	std::cout.write(reinterpret_cast<const char *>(bytes.data()),
 			bytes.size()) << std::flush;
-
 	return 0;
 }
 ```
 
-### Building
+#### C
+```c
+#include <base58check.h>
+
+#include <err.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sysexits.h>
+
+int main() {
+	// read a line from stdin
+	char *in = NULL;
+	ssize_t n_in = 0;
+	if ((n_in = getline(&in, (size_t *) &n_in, stdin)) < 0 && ferror(stdin))
+		err(EX_IOERR, "stdin");
+
+	// chop off any trailing newline character
+	if (n_in && in[n_in - 1] == '\n')
+		in[--n_in] = '\0';
+
+	// decode the Base58Check
+	unsigned char *out = NULL;
+	size_t n_out = 0;
+	if (base58check_decode(&out, &n_out, in, n_in, 0) < 0)
+		errx(EX_DATAERR, "base58check_decode failed");
+
+	// output the raw bytes
+	if (fwrite(out, 1, n_out, stdout) < n_out || fflush(stdout) < 0)
+		err(EX_IOERR, "stdout");
+
+	// be tidy
+	base58check_free(out);
+	free(in);
+	return EX_OK;
+}
+```
+
+## Building
 
 1. Install the prerequisites — most/all of which you probably already have: