C中带\ 0的字符串的长度 [英] Length of string with \0 in it in C

问题描述

我将用户的输入读为:

scanf("%[^\n]", message); 

现在我初始化char消息[100] ="";，在另一个函数中我需要找出消息中输入的长度，我很容易用strlen()做到了这一点，不幸的是，当我稍后在终端<中执行此操作时，它无法正常工作/p>

And I initialise char message [100] =""; now, in another function I need to find out length of input in message, I did it easily with strlen(), unfortunately it doesn't work correctly when I do later in terminal

echo -e "he\0llo" | .asciiart 50 

它将读取整个输入，但strlen仅返回长度2.

It will read the whole input BUT strlen will only return length 2.

还有其他方法可以找出输入的长度吗?

Is there any other way I could find out length of input ?

推荐答案

按定义 strlen 停在空字符上

在读取字符串后，您必须计数/最多读取EOF和/或换行符，而不是最多计数空字符

you have to count/read up to EOF and/or the newline rather than counting up to the null character after you read the string

如前所述，%n允许获取读取的字符数，例如:

As said in a remark %n allows to get the number of read characters, example :

#include <stdio.h>

int main()
{
  char message[100] = { 0 };
  int n;

  if (scanf("%99[^\n]%n", message, &n) == 1)
    printf("%d\n", n);
  else
    puts("empty line or EOF");
}

编译和执行:

pi@raspberrypi:/tmp $ gcc -g c.c
pi@raspberrypi:/tmp $ echo "" | ./a.out
empty line or EOF
pi@raspberrypi:/tmp $ echo -n "" | ./a.out
empty line or EOF
pi@raspberrypi:/tmp $ echo -e "he\0llo" | ./a.out
6
pi@raspberrypi:/tmp $ 

如您所见，无法区分空行和EOF(即使查看 errno )

As you can see it is not possible to distinguish an empty line and EOF (even looking at errno)

您也可以使用ssize_t getline(char **lineptr, size_t *n, FILE *stream);:

#include <stdio.h>
#include <stdlib.h>

int main()
{
  char *lineptr = NULL;
  size_t n = 0;
  ssize_t sz = getline(&lineptr, &n, stdin);

  printf("%zd\n", sz);

  free(lineptr);
}

但在这种情况下，可能的换行符已获取并计数:

but the possible newline is get and counted in that case :

pi@raspberrypi:/tmp $ gcc -pedantic -Wextra -g c.c
pi@raspberrypi:/tmp $ echo -e "he\0llo" | ./a.out
7
pi@raspberrypi:/tmp $ echo -e -n "he\0llo" | ./a.out
6
pi@raspberrypi:/tmp $ echo "" | ./a.out
1
pi@raspberrypi:/tmp $ echo -n "" | ./a.out
-1

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