[英]In C++ storing and retrieving of character vector (vector<char>) of all zero value (i.e. '\0' or string terminator) from file
Using fstream
I have created a file to store a fixed length sequence of zero value (0) ie '\0' ASCII code available in a character vector (vector).使用
fstream
我创建了一个文件来存储一个固定长度的零值 (0) 序列,即字符向量 (vector) 中可用的 '\0' ASCII 码。
fstream Fpt;
Fpt.open("Data.bin",ios::out|ios::binary);
std::vector<char> V;
char c=0;
for(int i=0;i<10;i++)V.push_back(c);
Fpt.write((char *)&V,10);
Fpt.close();
Fpt.open("Data.bin",ios::in | ios::out|ios::binary);
V.clear();
Fpt.read((char *)&V, 10);
for(auto v: V) printf("(%c,%d,%X)",v,v,v);
But the output is looking like (▌,-35,FFFFFFDD) (▌,-35,FFFFFFDD)...但是 output 看起来像 (▌,-35,FFFFFFDD) (▌,-35,FFFFFFDD)...
You write the vector object itself, not the data wrapped by the vector (which is located on the heap).您编写向量 object 本身,而不是向量包装的数据(位于堆上)。
You need to get a pointer to the data itself and write that:您需要获取指向数据本身的指针并写入:
Fpt.write(V.data(), V.size());
Similarly when you read the data, you need to read it into the wrapped data:同样,在读取数据时,需要将其读入包装好的数据中:
V = std::vector<char>(10); // Reset the vector, remembering to set its size
Fpt.read(V.data(), V.size());
This statement is not correct:这种说法是不正确的:
Fpt.write((char *)&V,10);
You are getting the address of the vector object V
which is stored on the stack.您正在获取存储在堆栈中的向量 object
V
的地址。 What you want is the address of the underlying buffer (stored on the heap) that V
points at and so you need to use the data
member function.您想要的是
V
指向的底层缓冲区(存储在堆上)的地址,因此您需要使用data
成员 function。
So instead do this:所以改为这样做:
Fpt.write( V.data(), 10 );
Or this:或这个:
Fpt.write( &V[0], 10 );
What you do here is a bad idea:你在这里做的是一个坏主意:
char c=0;
for ( int i = 0; i < 10; i++ ) V.push_back(c);
This will cause the vector to repeatedly reallocate its buffer once the size reaches capacity.一旦大小达到容量,这将导致向量重复重新分配其缓冲区。 This is bad in terms of performance.
这在性能方面很糟糕。
Instead, write it like:相反,把它写成:
std::vector<char> V(10);
Now V
will be initialized with 10 \0
characters.现在
V
将被初始化为 10 个\0
字符。 No need to use a loop to fill the container.无需使用循环来填充容器。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.