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发表于 2008-01-02 19:04 |只看该作者 |倒序浏览

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大家好，我写了个程序，作用是把一些文件进行base64编码并跟相关的字符封装起来返回。
主程序如下。但老是运行的时候出现段错误，我知道肯定是操作内存出了问题。可总不知道在什么地方，翻阅了一些基本知识，malloc后一定要进行free。
我想请教下面的问题：（不谈代码写的如何）
1、请各位指点下我这里内存操作是否正确，并指出原因；
2、(b_str=ss();的时候，看起来没有问题，事实上我也不清楚)我把b_str = ss(); 换成 b_str = base64_encode(str,len,&b_len); 运行就出现段错误,
我发现在换成 b_str = base64_encode(str,len,&b_len); 的时候，去掉free(str);便可以执行，不出现段错误，但结果似乎有点问题，即 puts(b_str);b_str输出后面似乎多了点字符。肯定是操作内存什么地方出错了

恳请各位帮忙！

附件是我的全部程序，解决了再送8分

int main(){
char *p[];
p[0] = "/www/b.c";
p[1] = "/www/c.c";
p[2] = "/www/encode.h";
attachment(p);
}
static char* attachment(char**f){
char **p,*str,filename[100],*ret;
long i = 1024,len=0;
int b_len;
char str1[SHORT_SIZE] = "Content-Type: application/octet-stream; name=\"";
char str2[SHORT_SIZE] = "\"\nContent-Transfer-Encoding: BASE64\nContent-Disposition: attachment; filename=\"";
FILE *fp;
if(f==NULL) return NULL;
p = f;
ret = (char*)malloc(1);
while(*p!=NULL){
      unsigned char *b_str;
      int j=0,k=0;
      str = (char*)malloc(sizeof(char)*i+1);
      bzero(str,i+1);
      fp = fopen(*p,"rb");
      if(!fp){
         printf("can not open file %s\n",*p);
         exit(0);
      }
      len += fread(str,sizeof(char),i,fp);
      while(!feof(fp)){  //    没有读完

         j++;
         str = (char*)realloc(str,i*j+1);
         len+=fread(str+i*j,sizeof(char),i,fp);
      }
      *(str+i*j) = '\0';
      bzero(filename,100);
      if(strrchr(*p,'/')!=0)
         strcpy(filename,strrchr(*p,'/')+1);
      else
         strcpy(filename,*p);
//       b_str = base64_encode(str,len,&b_len);

      b_str = ss();//  这行换成上面一句就出现段错误

      k       = strlen(ret)+b_len+strlen(filename)*2+5+strlen(str1)+strlen(str2);
      ret = (char*)realloc(ret,k+1);
      puts(b_str); //  问题2说的这里

      strcat(ret,str1);strcat(ret,filename);
      strcat(ret,str2);strcat(ret,filename);
      strcat(ret,"\"\n\n");strcat(ret,b_str);
      strcat(ret,"\n\n");*(ret+k) = '\0';
      free(b_str);
      free(str);
      len = 0;
      p++;
}
return ret;
}

char * ss(){
char *p;
p = (char*)malloc(101);
bzero(p,101);
strcpy(p,"okbt");
return p;
}

下面是base64_encode.c ,我从php原码里弄出来的。

#include "base64_encode.h"
static const char base64_table[] =
{ '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', '+', '/', '\0'
};

static const char base64_pad = '=';

static const short base64_reverse_table[256] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
-1,  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, -1, -1, -1, -1, -1,
-1, 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, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
};

unsigned char *base64_encode(const unsigned char *str, int length, int *ret_length)
{
const unsigned char *current = str;
unsigned char *p;
unsigned char *result;

if ((length + 2) < 0 || ((length + 2) / 3) >= (1 << (sizeof(int) * 8 - 2))) {
      if (ret_length != NULL) {
         *ret_length = 0;
      }
      return NULL;
}

result = (unsigned char *)malloc(((length + 2) / 3) * 4);
p = result;

while (length > 2) { /* keep going until we have less than 24 bits */
      *p++ = base64_table[current[0] >> 2];
      *p++ = base64_table[((current[0] & 0x03) << 4) + (current[1] >> 4)];
      *p++ = base64_table[((current[1] & 0x0f) << 2) + (current[2] >> 6)];
      *p++ = base64_table[current[2] & 0x3f];

      current += 3;
      length -= 3; /* we just handle 3 octets of data */
}

/* now deal with the tail end of things */
if (length != 0) {
      *p++ = base64_table[current[0] >> 2];
      if (length > 1) {
         *p++ = base64_table[((current[0] & 0x03) << 4) + (current[1] >> 4)];
         *p++ = base64_table[(current[1] & 0x0f) << 2];
         *p++ = base64_pad;
      } else {
         *p++ = base64_table[(current[0] & 0x03) << 4];
         *p++ = base64_pad;
         *p++ = base64_pad;
      }
}
if (ret_length != NULL) {
      *ret_length = (int)(p - result);
}
*p = '\0';
return result;
}

[ 本帖最后由 sunceenjoy 于 2008-1-2 19:07 编辑 ]