base64码简介
Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一，大家可以查看RFC2045～RFC2049，上面有MIME的详细规范。Base64编码可用于在HTTP环境下传递较长的标识信息。例如，在Java Persistence系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为128-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP GET URL中的参数。在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。此时，采用Base64编码具有不可读性，即所编码的数据不会被人用肉眼所直接看到。
0. 源数据都是8位位宽的数据；
1. 相当于分组码，将源数据分为3个一组，每一组共24bits，采用每6位对应一个编码码字，那么3*8bits = 4*6its, 将3个数据映射成4个数据，由于编码的码字都是6位长度，换位10进制就是0-63，总共有64中可能性，这也是base64名字的来历；
2. 6bits对应10进制数对应的码字如最后的表；
C代码编码
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#include <stdio.h>#include <string.h>// 全局常量定义const char * base64char = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";const char padding_char = '=';/*编码代码* const unsigned char * sourcedata， 源数组* char * base64 ，码字保存*/int base64_encode(const unsigned char * sourcedata, char * base64){ int i=0, j=0; unsigned char trans_index=0; // 索引是8位，但是高两位都为0 const int datalength = strlen((const char*)sourcedata); for (; i < datalength; i += 3){ // 每三个一组，进行编码 // 要编码的数字的第一个 trans_index = ((sourcedata[i] >> 2) & 0x3f); base64[j++] = base64char[(int)trans_index]; // 第二个 trans_index = ((sourcedata[i] << 4) & 0x30); if (i + 1 < datalength){ trans_index |= ((sourcedata[i + 1] >> 4) & 0x0f); base64[j++] = base64char[(int)trans_index]; }else{ base64[j++] = base64char[(int)trans_index]; base64[j++] = padding_char; base64[j++] = padding_char; break; // 超出总长度，可以直接break } // 第三个 trans_index = ((sourcedata[i + 1] << 2) & 0x3c); if (i + 2 < datalength){ // 有的话需要编码2个 trans_index |= ((sourcedata[i + 2] >> 6) & 0x03); base64[j++] = base64char[(int)trans_index]; trans_index = sourcedata[i + 2] & 0x3f; base64[j++] = base64char[(int)trans_index]; } else{ base64[j++] = base64char[(int)trans_index]; base64[j++] = padding_char; break; } } base64[j] = '\0'; return 0;} |
解码
包括两个函数：
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/** 在字符串中查询特定字符位置索引* const char *str ，字符串* char c，要查找的字符*/inline int num_strchr(const char *str, char c) // { const char *pindex = strchr(str, c); if (NULL == pindex){ return -1; } return pindex - str;}/* 解码* const char * base64 码字* unsigned char * dedata， 解码恢复的数据*/int base64_decode(const char * base64, unsigned char * dedata){ int i = 0, j=0; int trans[4] = {0,0,0,0}; for (;base64[i]!='\0';i+=4){ // 每四个一组，译码成三个字符 trans[0] = num_strchr(base64char, base64[i]); trans[1] = num_strchr(base64char, base64[i+1]); // 1/3 dedata[j++] = ((trans[0] << 2) & 0xfc) | ((trans[1]>>4) & 0x03); if (base64[i+2] == '='){ continue; } else{ trans[2] = num_strchr(base64char, base64[i + 2]); } // 2/3 dedata[j++] = ((trans[1] << 4) & 0xf0) | ((trans[2] >> 2) & 0x0f); if (base64[i + 3] == '='){ continue; } else{ trans[3] = num_strchr(base64char, base64[i + 3]); } // 3/3 dedata[j++] = ((trans[2] << 6) & 0xc0) | (trans[3] & 0x3f); } dedata[j] = '\0'; return 0;} |
下面是其他网友的补充可以参考一下
核心代码
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#include <stdio.h>#include <stdlib.h>#include <string.h>#include <ctype.h>static const char b64_table[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";static const char reverse_table[128] ={ 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64, 64, 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, 64, 64, 64, 64, 64, 64, 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, 64, 64, 64, 64, 64};unsigned char *base64_encode(unsigned char *bindata,size_t inlen,unsigned char **out,size_t *outlen){ size_t _outlen = *outlen; unsigned char *_out = NULL; size_t out_pos = 0; if(NULL == *out) { _outlen = (inlen / 3 + (inlen%3 != 0)) * 4 + 1; _out = malloc(_outlen); } else { _outlen = *outlen; _out = *out; } memset(_out,'=',_outlen); _out[_outlen-1] = 0; unsigned int bits_collected = 0; unsigned int accumulator = 0; for(int i = 0; i < inlen; i++) { accumulator = (accumulator << 8) | (bindata[i] & 0xffu); bits_collected += 8; while (bits_collected >= 6) { bits_collected -= 6; _out[out_pos++] = b64_table[(accumulator >> bits_collected) & 0x3fu]; } } if(bits_collected >= 6) { if(NULL == *out) { free(_out); } return NULL; } if (bits_collected > 0) { // Any trailing bits that are missing. accumulator <<= 6 - bits_collected; _out[out_pos++] = b64_table[accumulator & 0x3fu]; } *outlen = _outlen; *out = _out; return _out;}unsigned char *base64_decode(unsigned char *bindata,size_t inlen,unsigned char **out,size_t *outlen){ size_t _outlen = *outlen; unsigned char *_out = NULL; int bits_collected = 0; unsigned int accumulator = 0; size_t out_pos = 0; if(NULL == *out) { _outlen = inlen; _out = malloc(_outlen); } else { _outlen = *outlen; _out = *out; } int c = 0; for(int i = 0; i < inlen; i++) { c = bindata[i]; if (isspace(c) || c == '=') { // Skip whitespace and padding. Be liberal in what you accept. continue; } if ((c > 127) || (c < 0) || (reverse_table[c] > 63)) { return NULL; } accumulator = (accumulator << 6) | reverse_table[c]; bits_collected += 6; if (bits_collected >= 8) { bits_collected -= 8; _out[out_pos++] = (char)((accumulator >> bits_collected) & 0xffu); } } *outlen = _outlen; *out = _out; return _out;}int main(int argc,char *argv[]){ unsigned char *str = argv[1]; unsigned char *out = 0; size_t len = 0; printf("%s\n",base64_encode(str,strlen(str),&out,&len)); unsigned char *_out = 0; size_t _len = 0; printf("%s\n",base64_decode(out,strlen(out),&_out,&_len)); return 0;} |
这篇C语言base64编解码的文章就介绍到这了，希望大家以后多多支持服务器之家。
