base64 算法实现（收集网络中好的代码）

base64 算法实现（收集网络中好的代码）

1. 第一种 c++实现

const char base64_table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

std::string base64_encode(const char* input, int length) {
	std::string output;

	for (int i = 0; i < length; i += 3) {
		int c1 = input[i];
		int c2 = i + 1 < length ? input[i + 1] : 0;
		int c3 = i + 2 < length ? input[i + 2] : 0;

		int index1 = (c1 >> 2) & 0x3f;
		int index2 = ((c1 & 0x3) << 4) | ((c2 >> 4) & 0xf);
		int index3 = ((c2 & 0xf) << 2) | ((c3 >> 6) & 0x3);
		int index4 = c3 & 0x3f;

		output += base64_table[index1];
		output += base64_table[index2];
		output += i + 1 < length ? base64_table[index3] : '=';
		output += i + 2 < length ? base64_table[index4] : '=';
	}

	return output;
}

2. 第二种 c语言实现

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

char base64_chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

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

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

    // 补充末尾的填充字符 '='
    for (size_t i = 0; i < (3 - input_length % 3) % 3; i++) {
        encoded_data[output_length - 1 - i] = '=';
    }

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

int main() {
    unsigned char input[100];
    printf("请输入要进行Base64编码的字符串: ");
    fgets(input, sizeof(input), stdin);
    input[strcspn(input, "\n")] = '\0';

    char* encoded = base64_encode(input, strlen(input));
    printf("Base64编码结果: %s\n", encoded);

    free(encoded);
    return 0;
}