C语言 如何使用 read() 读取数据直到文件结束？
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How to use read() to read data until the end of the file?
提问by sekmet64
I'm trying to read binary data in a C program with read() but EOF test doesn't work. Instead it keeps running forever reading the last bit of the file.
我正在尝试使用 read() 读取 C 程序中的二进制数据，但 EOF 测试不起作用。相反，它会一直运行读取文件的最后一位。
#include <stdio.h>
#include <fcntl.h>
int main() {
// writing binary numbers to a file
int fd = open("afile", O_WRONLY | O_CREAT, 0644);
int i;
for (i = 0; i < 10; i++) {
write(fd, &i, sizeof(int));
}
close(fd);
//trying to read them until EOF
fd = open("afile", O_RDONLY, 0);
while (read(fd, &i, sizeof(int)) != EOF) {
printf("%d", i);
}
close(fd);
}
回答by Jerry Coffin
readreturns the number of characters it read. When it reaches the end of the file, it won't be able to read any more (at all) and it'll return 0, not EOF.
read返回它读取的字符数。当它到达文件末尾时，它将无法再读取（根本无法读取）并且将返回 0，而不是 EOF。
回答by u0b34a0f6ae
You must check for errors. On some (common) errors you want to call read again!
您必须检查错误。对于某些（常见）错误，您想再次调用 read！
If read() returns -1 you have to check errnofor the error code. If errno equals either EAGAINor EINTR, you want to restart the read()call, without using its (incomplete) returned values. (On other errors, you maybe want to exit the program with the appropriate error message (from strerror))
如果 read() 返回 -1，则必须检查errno错误代码。如果 errno 等于EAGAIN或EINTR，则您希望重新启动read()调用，而不使用其（不完整的）返回值。（对于其他错误，您可能希望使用适当的错误消息（来自 strerror）退出程序）
