Base64 编解码C语言实现

具体代码如下:

#

include <stdio.h> 
const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="; 
char* base64_encode(const char* data, int data_len); 
char *base64_decode(const char* data, int data_len); 
static char find_pos(char ch); 
int main(int argc, char* argv[]) 
{ 
    char *t = "那个abcd你好吗，哈哈，ANMOL"; 
    int i = 0; 
    int j = strlen(t); 
    char *enc = base64_encode(t, j); 
    int len = strlen(enc); 
    char *dec = base64_decode(enc, len); 
    printf("\noriginal: %s\n", t); 
    printf("\nencoded : %s\n", enc); 
    printf("\ndecoded : %s\n", dec); 
    free(enc); 
    free(dec); 
    return 0; 
} 
/* */ 
char *base64_encode(const char* data, int data_len) 
{ 
    //int data_len = strlen(data); 
    int prepare = 0; 
    int ret_len; 
    int temp = 0; 
    char *ret = NULL; 
    char *f = NULL; 
    int tmp = 0; 
    char changed[4]; 
    int i = 0; 
    ret_len = data_len / 3; 
    temp = data_len % 3; 
    if (temp > 0) 
    { 
        ret_len += 1; 
    } 
    ret_len = ret_len*4 + 1; 
    ret = (char *)malloc(ret_len); 
      
    if ( ret == NULL) 
    { 
        printf("No enough memory.\n"); 
        exit(0); 
    } 
    memset(ret, 0, ret_len); 
    f = ret; 
    while (tmp < data_len) 
    { 
        temp = 0; 
        prepare = 0; 
        memset(changed, '\0', 4); 
        while (temp < 3) 
        { 
            //printf("tmp = %d\n", tmp); 
            if (tmp >= data_len) 
            { 
                break; 
            } 
            prepare = ((prepare << 8) | (data[tmp] & 0xFF)); 
            tmp++; 
            temp++; 
        } 
        prepare = (prepare<<((3-temp)*8)); 
        //printf("before for : temp = %d, prepare = %d\n", temp, prepare); 
        for (i = 0; i < 4 ;i++ ) 
        { 
            if (temp < i) 
            { 
                changed[i] = 0x40; 
            } 
            else 
            { 
                changed[i] = (prepare>>((3-i)*6)) & 0x3F; 
            } 
            *f = base[changed[i]]; 
            //printf("%.2X", changed[i]); 
            f++; 
        } 
    } 
    *f = '\0'; 
      
    return ret; 
      
} 
/* */ 
static char find_pos(char ch)   
{ 
    char *ptr = (char*)strrchr(base, ch);//the last position (the only) in base[] 
    return (ptr - base); 
} 
/* */ 
char *base64_decode(const char *data, int data_len) 
{ 
    int ret_len = (data_len / 4) * 3; 
    int equal_count = 0; 
    char *ret = NULL; 
    char *f = NULL; 
    int tmp = 0; 
    int temp = 0; 
    char need[3]; 
    int prepare = 0; 
    int i = 0; 
    if (*(data + data_len - 1) == '=') 
    { 
        equal_count += 1; 
    } 
    if (*(data + data_len - 2) == '=') 
    { 
        equal_count += 1; 
    } 
    if (*(data + data_len - 3) == '=') 
    {//seems impossible 
        equal_count += 1; 
    } 
    switch (equal_count) 
    { 
    case 0: 
        ret_len += 4;//3 + 1 [1 for NULL] 
        break; 
    case 1: 
        ret_len += 4;//Ceil((6*3)/8)+1 
        break; 
    case 2: 
        ret_len += 3;//Ceil((6*2)/8)+1 
        break; 
    case 3: 
        ret_len += 2;//Ceil((6*1)/8)+1 
        break; 
    } 
    ret = (char *)malloc(ret_len); 
    if (ret == NULL) 
    { 
        printf("No enough memory.\n"); 
        exit(0); 
    } 
    memset(ret, 0, ret_len); 
    f = ret; 
    while (tmp < (data_len - equal_count)) 
    { 
        temp = 0; 
        prepare = 0; 
        memset(need, 0, 4); 
        while (temp < 4) 
        { 
            if (tmp >= (data_len - equal_count)) 
            { 
                break; 
            } 
            prepare = (prepare << 6) | (find_pos(data[tmp])); 
            temp++; 
            tmp++; 
        } 
        prepare = prepare << ((4-temp) * 6); 
        for (i=0; i<3 ;i++ ) 
        { 
            if (i == temp) 
            { 
                break; 
            } 
            *f = (char)((prepare>>((2-i)*8)) & 0xFF); 
            f++; 
        } 
    } 
    *f = '\0'; 
    return ret; 
}

这里添加了两个方法find_pos和base64_decode。前者是寻找给定字符在base数组中的位置的，使用了strrchr函数，寻找字符在字符串中最后一次的位置，由于总会存在并且仅存在一次，所以函数结果直接使用。base64_decode函数里边跟encode函数差不多，我没有作注释。

对于代码中给定的串，运行结果如下：

original: 那个abcd你好吗，哈哈，ANMOL

encoded : xMe49mFiY2TE47rDwvCjrLn+uf6jrEFOTU9M

decoded : 那个abcd你好吗，哈哈，ANMOL