Base64的C语言实现_base64 c语言

Base64相比于16进制hex码，更加陌生一些，其实原理相通，都是把二进制字节流转换为明文字符串。

16进制Hex码就是Base16，取16个字符0123456789abcdef，每2个字符表示1个字节;

Base64取64个字符ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/

每4个字符表示3个字节。

本文给出Base64的C语言实现

Base64编码

const char base64_table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
int base64_encode(const unsigned char *data, size_t input_length, char *encoded_data, int size_buf) {
    int output_length = 4 * ((input_length + 2) / 3);
    if(size_buf < output_length)
    	return 0;
    
    if (encoded_data == NULL)
		return 0;
	int i;
	int j;
	
    for (i = 0, j = 0; i < input_length;) {
        unsigned int octet_a = i < input_length ? data[i++] : 0;
        unsigned int octet_b = i < input_length ? data[i++] : 0;
        unsigned int octet_c = i < input_length ? data[i++] : 0;
 
        unsigned int triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;
 
        encoded_data[j++] = base64_table[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = base64_table[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = base64_table[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = base64_table[(triple >> 0 * 6) & 0x3F];
    }
 
    for (i = 0; i < (3 - input_length % 3) % 3; i++) {
        encoded_data[output_length - 1 - i] = '=';
    }
 
    encoded_data[output_length] = '\0';
    return output_length;
}

Base64解码，字码表base64_table与Base64编码相同

int base64_decode_char(char c) 
{
	// strchr(base64_table, c) - base64_table;
	
    if (c >= 'A' && c <= 'Z') return c - 'A';
    if (c >= 'a' && c <= 'z') return c - 'a' + 26;
    if (c >= '0' && c <= '9') return c - '0' + 52;
    if (c == '+') return 62;
    if (c == '/') return 63;
    if (c == '=') return 0;
    
    return -1; // Invalid character
}
 
int base64_decode(const char *base64_string, unsigned char *decoded_data, int size_buf) 
{
	int input_length = strlen(base64_string);
	int output_length;
	
    if (input_length % 4 != 0)
		return 0; // Invalid input length
 
    output_length = input_length / 4 * 3;
    if (base64_string[input_length - 1] == '=') (output_length)--;
    if (base64_string[input_length - 2] == '=') (output_length)--;
    if(size_buf < output_length)
    	return 0;
	int i;
	int j;
	
    for (i = 0, j = 0; i < input_length;) {
        unsigned int sextet_a = base64_decode_char(base64_string[i++]);
        unsigned int sextet_b = base64_decode_char(base64_string[i++]);
        unsigned int sextet_c = base64_decode_char(base64_string[i++]);
        unsigned int sextet_d = base64_decode_char(base64_string[i++]);
 
        if (sextet_a == -1 || sextet_b == -1 || sextet_c == -1 || sextet_d == -1) {
            return 0; // Invalid character
        }
 
        unsigned int triple = (sextet_a << 3 * 6) + (sextet_b << 2 * 6) + (sextet_c << 1 * 6) + (sextet_d << 0 * 6);
 
        if (j < output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        if (j < output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        if (j < output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
    }
 
    return output_length;
}

测试

int main() 
{
	
	// Base64 编码  =================================
	char base64String[1000] = {0};
	
	//unsigned char byteArray[] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0xFF}; // 字节数组
	unsigned char byteArray[] = "hello world";
	
    int byteArrayLength = sizeof(byteArray) / sizeof(byteArray[0]);
    base64_encode(byteArray, byteArrayLength, base64String, sizeof(base64String));
    printf("Eecoded String: %s\n", base64String);
    
    
    // Base64 解码 =================================
    int i;
    unsigned char decodedByteArray[1000];
    
    //char *base64String = "SGVsbG8gV29ybGQh"; // Base64 编码的字符串
    //char *base64String = "AQIDBAUGBwgJCgsMDQ4PEBESExQVFhcYGRobHB0eHyAhIiMkJSYnKCkqKywtLi8wMTI=";
    int actualDecodedLength = base64_decode(base64String, decodedByteArray, sizeof(decodedByteArray));
 
    // 打印解码后的字节数组
    printf("Decoded Byte Array: ");
    for (i = 0; i < actualDecodedLength; i++) 
	{
        printf("%02X ", decodedByteArray[i]);
    }
    printf("\n");
	for (i = 0; i < actualDecodedLength; i++) 
	{
        printf("%c", decodedByteArray[i]);
    }
    printf("\n");
 
    return 0;
}