c base64代码

当然，我可以提供一些关于C语言中Base64编码和解码的代码示例。以下是一个简单的示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static const char base64_chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

char *base64_encode(const unsigned char *input, size_t length) {
    size_t encoded_length = 4 * ((length + 2) / 3);
    char *encoded_data = (char *) malloc(encoded_length + 1);
    if (encoded_data == NULL) {
        return NULL;
    }

    size_t i, j;
    for (i = 0, j = 0; i < length;) {
        uint32_t octet_a = i < length ? input[i++] : 0;
        uint32_t octet_b = i < length ? input[i++] : 0;
        uint32_t octet_c = i < length ? input[i++] : 0;

        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

        encoded_data[j++] = base64_chars[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = base64_chars[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = base64_chars[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = base64_chars[(triple >> 0 * 6) & 0x3F];
    }

    for (i = 0; i < (3 - length % 3) % 3; i++) {
        encoded_data[encoded_length - 1 - i] = '=';
    }

    encoded_data[encoded_length] = '\0';
    return encoded_data;
}

unsigned char *base64_decode(const char *input, size_t *length) {
    size_t input_length = strlen(input);
    if (input_length % 4 != 0) {
        return NULL;
    }

    size_t decoded_length = input_length / 4 * 3;
    if (input[input_length - 1] == '=') {
        decoded_length--;
    }
    if (input[input_length - 2] == '=') {
        decoded_length--;
    }

    unsigned char *decoded_data = (unsigned char *) malloc(decoded_length);
    if (decoded_data == NULL) {
        return NULL;
    }

    size_t i, j;
    for (i = 0, j = 0; i < input_length;) {
        uint32_t sextet_a = input[i] == '=' ? 0 & i++ : base64_chars[(size_t) input[i++]];
        uint32_t sextet_b = input[i] == '=' ? 0 & i++ : base64_chars[(size_t) input[i++]];
        uint32_t sextet_c = input[i] == '=' ? 0 & i++ : base64_chars[(size_t) input[i++]];
        uint32_t sextet_d = input[i] == '=' ? 0 & i++ : base64_chars[(size_t) input[i++]];

        uint32_t triple = (sextet_a << 3 * 6)
                          + (sextet_b << 2 * 6)
                          + (sextet_c << 1 * 6)
                          + (sextet_d << 0 * 6);

        if (j < decoded_length) {
            decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        }
        if (j < decoded_length) {
            decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        }
        if (j < decoded_length) {
            decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
        }
    }

    *length = decoded_length;
    return decoded_data;
}

int main() {
    const char *input = "Hello, World!";
    size_t input_length = strlen(input);

    char *encoded_data = base64_encode((const unsigned char *) input, input_length);
    printf("Encoded data: %s\n", encoded_data);

    size_t decoded_length;
    unsigned char *decoded_data = base64_decode(encoded_data, &decoded_length);
    printf("Decoded data: %.*s\n", (int) decoded_length, decoded_data);

    free(encoded_data);
    free(decoded_data);

    return 0;
}

这个示例包含了Base64编码和解码的函数。在`main`函数中，我们使用示例字符串"Hello, World!"进行编码和解码，并打印结果。

请注意，由于Base64编码后的数据是ASCII字符，编码后的数据可能会比原始数据更长。因此，对于编码后的数据，我们需要分配足够的内存空间。

希望这个例子能对你有所帮助！如果你有任何其他问题，请随时提问。