Zi 字媒體

純C 字串 BASE64 互轉/轉換 (C_Base64) 資料來源:https://www.jianshu.com/p/125c4bbed460 GITHUB: https://github.com/jash-git/C_Base64 字串長度變化規則: 設字串長度為n ，長度為 ⌈n/3⌉ *4    ⌈⌉  代表上取整 #include #include #include "base64.h" //https://www.jianshu.com/p/125c4bbed460 int main() { // insert code here... char str1[] = "tablename"; char str2[200] = {0}; //注意长度要给够 int len = 0; base64_encode(str1,(int)strlen(str1),str2,&len); printf("%s, len = %d\n", str2, len); char str3[200] = {0}; base64_decode(str2, (int)strlen(str2), str3, &len); printf("%s, len = %d\n", str3, len); return 0; } #ifndef BASE64_H_INCLUDED #define BASE64_H_INCLUDED #include #if __cplusplus extern "C"{ #endif int base64_encode(const char *indata, int inlen, char *outdata, int *outlen); int base64_decode(const char *indata, int inlen, char *outdata, int *outlen); #if __cplusplus } #endif #endif // BASE64_H_INCLUDED // // base64.c // base64 // // Created by guofu on 2017/5/25. // Copyright © 2017年 guofu. All rights reserved. // /** * 转解码过程 * 3 * 8 = 4 * 6; 3字节占24位, 4*6=24 * 先将要编码的转成对应的ASCII值 * 如编码: s 1 3 * 对应ASCII值为: 115 49 51 * 对应二进制为: 01110011 00110001 00110011 * 将其6个分组分4组: 011100 110011 000100 110011 * 而计算机是以8bit存储, 所以在每组的高位补两个0如下: * 00011100 00110011 00000100 00110011对应:28 51 4 51 * 查找base64 转换表 对应 c z E z * * 解码 * c z E z * 对应ASCII值为 99 122 69 122 * 对应表base64_suffix_map的值为 28 51 4 51 * 对应二进制值为 00011100 00110011 00000100 00110011 * 依次去除每组的前两位, 再拼接成3字节 * 即: 01110011 00110001 00110011 * 对应的就是s 1 3 */ #include "base64.h" #include #include // base64 转换表, 共64个 static const char base64_alphabet[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'}; // 解码时使用 static const unsigned char base64_suffix_map[256] = { 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 253, 255, 255, 253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 255, 255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 254, 255, 255, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255, 255, 255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255 }; static char cmove_bits(unsigned char src, unsigned lnum, unsigned rnum) { src <<= lnum; // src = src << lnum; src >>= rnum; // src = src >> rnum; return src; } int base64_encode(const char *indata, int inlen, char *outdata, int *outlen) { int ret = 0; // return value if (indata == NULL || inlen == 0) { return ret = -1; } int in_len = 0; // 源字符串长度, 如果in_len不是3的倍数, 那么需要补成3的倍数 int pad_num = 0; // 需要补齐的字符个数, 这样只有2, 1, 0(0的话不需要拼接, ) if (inlen % 3 != 0) { pad_num = 3 - inlen % 3; } in_len = inlen + pad_num; // 拼接后的长度, 实际编码需要的长度(3的倍数) int out_len = in_len * 8 / 6; // 编码后的长度 char *p = outdata; // 定义指针指向传出data的首地址 //编码, 长度为调整后的长度, 3字节一组 int i; for (i = 0; i < in_len; i+=3) { int value = *indata >> 2; // 将indata第一个字符向右移动2bit(丢弃2bit) char c = base64_alphabet[value]; // 对应base64转换表的字符 *p = c; // 将对应字符(编码后字符)赋值给outdata第一字节 //处理最后一组(最后3字节)的数据 if (i == inlen + pad_num - 3 && pad_num != 0) { if(pad_num == 1) { *(p + 1) = base64_alphabet[(int)(cmove_bits(*indata, 6, 2) + cmove_bits(*(indata + 1), 0, 4))]; *(p + 2) = base64_alphabet[(int)cmove_bits(*(indata + 1), 4, 2)]; *(p + 3) = '='; } else if (pad_num == 2) { // 编码后的数据要补两个 '=' *(p + 1) = base64_alphabet[(int)cmove_bits(*indata, 6, 2)]; *(p + 2) = '='; *(p + 3) = '='; } } else { // 处理正常的3字节的数据 *(p + 1) = base64_alphabet[cmove_bits(*indata, 6, 2) + cmove_bits(*(indata + 1), 0, 4)]; *(p + 2) = base64_alphabet[cmove_bits(*(indata + 1), 4, 2) + cmove_bits(*(indata + 2), 0, 6)]; *(p + 3) = base64_alphabet[*(indata + 2) & 0x3f]; } p += 4; indata += 3; } if(outlen != NULL) { *outlen = out_len; } return ret; } int base64_decode(const char *indata, int inlen, char *outdata, int *outlen) { int ret = 0; if (indata == NULL || inlen <= 0 || outdata == NULL || outlen == NULL) { return ret = -1; } if (inlen % 4 != 0) { // 需要解码的数据不是4字节倍数 return ret = -2; } int t = 0, x = 0, y = 0, i = 0; unsigned char c = 0; int g = 3; while (indata[x] != 0) { // 需要解码的数据对应的ASCII值对应base64_suffix_map的值 c = base64_suffix_map[indata[x++]]; if (c == 255) return -1;// 对应的值不在转码表中 if (c == 253) continue;// 对应的值是换行或者回车 if (c == 254) { c = 0; g--; }// 对应的值是'=' t = (t<<6) | c; // 将其依次放入一个int型中占3字节 if (++y == 4) { outdata[i++] = (unsigned char)((t>>16)&0xff); if (g > 1) outdata[i++] = (unsigned char)((t>>8)&0xff); if (g > 2) outdata[i++] = (unsigned char)(t&0xff); y = t = 0; } } if (outlen != NULL) { *outlen = i; } return ret; }