c语言base64加解密

C语言中没有内置的Base64加解密函数，但可以通过调用第三方库来实现。

一个常用的第三方库是openssl，使用它可以很方便地进行Base64编码和解码。

以下是一个示例程序，展示了如何使用openssl库进行Base64编码和解码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/bio.h>
#include <openssl/evp.h>

int base64_encode(const char *input, int input_len, char *output, int output_size)
{
    BIO *bmem = NULL;
    BIO *b64 = NULL;
    BUF_MEM *bptr = NULL;

    b64 = BIO_new(BIO_f_base64());
    if (b64 == NULL) {
        return -1;
    }

    bmem = BIO_new(BIO_s_mem());
    if (bmem == NULL) {
        BIO_free(b64);
        return -1;
    }

    b64 = BIO_push(b64, bmem);
    BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);

    if (BIO_write(b64, input, input_len) <= 0) {
        BIO_free_all(b64);
        return -1;
    }

    if (BIO_flush(b64) <= 0) {
        BIO_free_all(b64);
        return -1;
    }

    BIO_get_mem_ptr(b64, &bptr);
    if (bptr->length > output_size) {
        BIO_free_all(b64);
        return -1;
    }

    memcpy(output, bptr->data, bptr->length);
    output[bptr->length] = '\0';

    BIO_free_all(b64);

    return bptr->length;
}

int base64_decode(const char *input, int input_len, char *output, int output_size)
{
    BIO *bmem = NULL;
    BIO *b64 = NULL;

    b64 = BIO_new(BIO_f_base64());
    if (b64 == NULL) {
        return -1;
    }

    bmem = BIO_new_mem_buf((void *)input, input_len);
    if (bmem == NULL) {
        BIO_free(b64);
        return -1;
    }

    bmem = BIO_push(b64, bmem);

    int len = BIO_read(bmem, output, output_size);
    if (len < 0) {
        BIO_free_all(bmem);
        return -1;
    }

    output[len] = '\0';

    BIO_free_all(bmem);

    return len;
}

int main()
{
    char input[] = "hello world";
    char encoded[100];
    char decoded[100];

    printf("Original: %s\n", input);

    int len = base64_encode(input, strlen(input), encoded, sizeof(encoded));
    printf("Encoded: %s (%d)\n", encoded, len);

    len = base64_decode(encoded, len, decoded, sizeof(decoded));
    printf("Decoded: %s (%d)\n", decoded, len);

    return 0;
}

运行结果如下：

Original: hello world
Encoded: aGVsbG8gd29ybGQ= (16)
Decoded: hello world (11)