多余的乱码为什么打印？ [英] Why are extra garbage characters printed?

问题描述

我尝试使用read（），以获得从文件中的某些字符只是为了学习这个API。我创建一个在同一目录中名为文件的文件，它是内容：

I try to use read() to get some characters from file just for learning this API. I have create a file called "file" in the same directory and it is content:

1:2:ab:cd:ef

下面是code：

#include <stdio.h>
#include <error.h>

int read_indent(int sockfd){
  int sport, cport;
  char user[3], rtype[3], addinfo[3];
  char buffer[4+4+3+3+3+1];

  if(read(sockfd, buffer, sizeof(buffer)) <= 0) {
    perror("read: %m");
    return -1;
  }

  buffer[sizeof(buffer)-1] = '\0';

  sscanf(buffer, "%d:%d:%s:%s:%s", &sport, &cport, rtype, user, addinfo);
  printf("%d:%d:%s:%s:%s", sport, cport, rtype, user, addinfo);
  return 0;
}

int main(){
  FILE *file_pt = fopen("file", "r");
  if(file_pt == NULL) { printf("fopen error\n"); return -1;}
  char buf[128];
  int a = read_indent(fileno(file_pt));
  fclose(file_pt);
  return 0;
}

我的printf返回我

My printf returns me

1:2:ab:cd:ef::xPvx

其中， X 是一些垃圾字符我无法识别。究竟是什么原因呢？ INT 为4个字节在我的系统。

where x is some garbage character I cannot recognize. What is the reason for this? int is 4 bytes in my system.

推荐答案

一个问题是，你没有指定％S 参数的宽度。这意味着，它匹配，直到第一空白字符。有你的字符串中没有空白字符，所以第一个％S 匹配到最后，​​你的字符串，以填补其他变量后只留下垃圾数据。

One issue is that you didn't specify a width for the %s parameters. This means that it matches up until the first whitespace character. There are no whitespace characters in your string, so the first %s matches until the end, leaving only garbage data after your string to fill the other variables.

试试这个：

sscanf(buffer, "%d:%d:%2s:%2s:%2s", &sport, &cport, rtype, user, addinfo);

另一个问题是，你不空终止缓冲正常，读返回的字符数读 - 后添加一个空

The other issue is that you don't null-terminate your buffer properly, read returns the number of characters read - add a null after that.

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