[英]linux read() function from unistd.h doesn't work for me :(
[英]unistd read() doesn't work
我正在尝试使用unistd库编写/读取文本文件。 稍后,我将其部署到/ dev路径中的文件中。 我正在尝试使用std::vector
类型代替char buffer[]
。 所以我写了两个实现,一个使用向量,另一个使用char缓冲区。 两者都可以很好地在文件中写入,但是都不能读取文件。
这是我的测试代码:
使用char的缓冲区
void tests_using_buffer_of_char(const std::string &path)
{
int file_descriptor_char;
char buffer[8] ={0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08};
std::cout << sizeof(buffer) << std::endl;
for(auto i = 0; i < sizeof(buffer); i++)
std::cout << buffer[i] << std::endl;
file_descriptor_char = open(path.c_str(), O_RDWR);
if(file_descriptor_char != -1)
std::cout << "open with success " << path << std::endl;
std::size_t size = strlen(buffer);
ssize_t write_bytes = write(file_descriptor_char, buffer, size);
std::cout << size << " <-- size of buffer " << write_bytes << " <-- size of writed bytes" << std::endl;
memset(&buffer[0], 0, sizeof(buffer));
ssize_t read_bytes = read(file_descriptor_char, &buffer, size);
std::cout << size << " <-- size of buffer " << read_bytes << " <-- size of readed bytes" << std::endl;
for(auto i = 0; i < sizeof(buffer); i++)
std::cout << buffer[i] << std::endl;
if(close(file_descriptor_char) != -1)
std::cout << "close with success "<< path << std::endl;
}
使用向量缓冲区
void tests_using_buffer_of_vector(const std::string &path)
{
int file_descriptor_vector;
std::vector<char> buffer = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08};
std::cout << buffer.size() << std::endl;
for(auto i : buffer)
std::cout << i << std::endl;
file_descriptor_vector = open(path.c_str(), O_RDWR);
if(file_descriptor_vector != -1)
std::cout << "open whit success " << path << std::endl;
ssize_t write_bytes = write(file_descriptor_vector, buffer.data(), buffer.size());
std::cout << buffer.size() << " <-- size of buffer " << write_bytes << " <-- size of writed bytes" << std::endl;
buffer.clear();
ssize_t read_bytes = read(file_descriptor_vector, buffer.data(), write_bytes);
std::cout << buffer.size() << " <-- size of buffer " << read_bytes << " <-- size of readed bytes" << std::endl;
for(auto i : buffer)
std::cout << i << std::endl;
if(close(file_descriptor_vector) != -1)
std::cout << "close with success " << path << std::endl;
}
感谢大家!
您必须将文件描述符重置为文件的开头,然后再使用它进行写入后再尝试将其用于读取。 您可以关闭文件然后重新打开它,也可以从头开始。
lseek(file_descriptor_vector, SEEK_SET, 0);
在读入向量之前,请不要清除它。 clear
方法将实质上释放与向量关联的内存。
1]只需使用fclose
并重新打开文件即可。
2] fseek(fp, 0, SEEK_SET);
3] rewind(fp);
您使用file pointer
文件的末尾。
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