如何正确错误地读取C中的陷阱以从文件描述符中获取字节数 [英] How to properly error trap read in c to get byte number from a file descriptor
问题描述
我目前正在编写一个小型虚拟程序,以尝试使用读入c来正确地解决问题.我做了一个小的函数readdata,从文件描述符中读取并存储在缓冲区中,然后返回读取的字节数.我的问题是我正在尝试正确地处理错误并捕获错误,以便没有缓冲区溢出,但我一直在做一些事情.
I am currently writing a small dummy program to try and get the hang of properly using the read in c. I made a small function called readdata to read from the file descriptor and store in a buffer then return the number of bytes read. My problem is I am trying to correctly error handle and trap things so that there is no buffer overflow but I keep doing something from.
这是测试人员:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define BUFSIZE 10
int readdata(int fd, char *buf, int bsize);
int main(void) {
char buf[BUFSIZE];
int returnval;
int length;
returnval = readdata(STDIN_FILENO, buf, BUFSIZE);
printf("%s",buf);
length = strlen(buf);
fprintf(stderr,"The return value is %d\n", returnval);
fprintf(stderr,"The string is %s\n",buf);
fprintf(stderr,"The length of the string is %d\n",length);
return 0;
}
这是小功能:
#include <stdio.h>
#include <stdlib.h>
int readdata(int fd, char *buf, int bufsize){
int n = 0;
if(fd < 0){
return 1;
}
while((n=read(fd,buf,(bufsize-1)))>0){
if(n == -1) {
perror( "Read failed" );
return 1;
}
else{
buf[bufsize] = 0;
return n;
}
}
}
如果我运行
cc -o test test.c readdata.c
然后放
echo "Hello" | ./test
工作正常.但是,如果我通过bufsize限制,如下所示:
It works fine. But if I pass the bufsize limit like this:
echo "1234567891" | ./getdatatest
它给了我这个奇怪的输出,上面写着字符串是123456789 [一些奇怪的符号]".因此,我不确定在哪里处理此错误,或者为什么在读取时仍然错误地将其放入缓冲区.
It gives me this weird output where it says "the string is 123456789[some weird symbol]" . So I am not sure where to handle this error or why it is still incorrectly putting in the buffer when reading.
推荐答案
您知道read()
返回的字符少于您请求的字符吗?另外,buf[bufsize]
刚好在buf
的结尾.您的readdata
函数还应该在发生错误时返回类似-1
的信息,而不是返回1
,以便您可以区分条件读取一个字节"与"IO错误".
You do know that read()
can return less characters than you requested? Also, buf[bufsize]
is just past the end of buf
. Your readdata
function should also return something like -1
on error instead of 1
so you can distinguish the condition "one byte read" from "IO error."
考虑这样的事情:
for (;;) {
n = read(fd, buf, (bufsize - 1));
if(n == -1) {
perror( "Read failed" );
return -1;
} else {
buf[n] = 0;
return n;
}
}
这篇关于如何正确错误地读取C中的陷阱以从文件描述符中获取字节数的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!