Question

我正在测试一个自定义结构，其中有bitfield和unsigned char *（将在稍后分配）。

这是结构：

struct test {
  unsigned int field1 : 1;
  unsigned int field2 : 15;
  unsigned int field3 : 32;
  unsigned int dataLength : 16;
  unsigned char * data;
}

问题是当我尝试将此结构保存在十六进制文件中时。

例如：

int writeStruct(struct test *ptr, FILE *f) {

   // for data, suppose I know the length by dataLength  : 
   // this throw me : cannot take adress of bit field
   int count;
   count = fwrite( &(ptr->field2), sizeof(unsigned int), 1, f);

   // this throw me : makes pointer to integer without a cast
   count = fwrite( ptr->field2, sizeof(unsigned int), 1, f);

   // same for length
   count = fwrite( htons(ptr->data) , ptr->dataLength, 1,f);       

   // so , how to do that ?
}

同样的问题是fread：

int readAnStructFromFile(struct test *ptr, FILE *f) {
   // probably wrong
   fread(ptr->field1, sizeof(unsigned int), 1, f);
}

那么，我怎么能像这样写/读结构？

感谢您的帮助

PS for fread，如果没有这些位域，这可能会有效：How to fread() structs?

Answer 1

无法获取位域的地址。处理它的常用方法是在读/写端使用临时变量，或者只是将整个结构保存为单个实体。对于临时变量，它看起来如下：

int count;
int field2 = ptr->field2;
count = fwrite( &field2, sizeof(unsigned int), 1, f);
...
int field1;
fread(&field1, sizeof(unsigned int), 1, f);
ptr->field1 = field1;

或整个结构：

count = fwrite( ptr, sizeof(struct test), 1, f);

带有位域和字符*的fwrite / fread结构

1 个答案: