用C中的空格读取字符串 [英] Reading in a string with spaces in C

问题描述

我正在尝试读取可能包含或不包含空格的字符串.你好，世界".通过对用户输入的数字选择菜单进行以下操作.这只是我正在尝试做的一小部分复制品.

I am trying to read in a string that may or may not include spaces ex. "hello world". By doing the following with a number select menu that is inputted by the user. This is just a small replica of what I am trying to do.

#include <stdio.h>
#include <string.h>

int main(void){
  char line[3][80];

  strcpy(line[0],"default line 1\n");
  strcpy(line[1],"default line 2\n");
  strcpy(line[2],"default line 3\n");

  for(int i = 0; i < 3; i++){
    printf("%s", line[i]);
  }

  int option = 0;
  printf("would you like to replace line 1? (1 for yes)\n");
  scanf("%d",&option);
  if(option==1){
   printf("what would you like to replace the line with?\n");
   fgets(line[0],strlen(line[0]),stdin);
  }

  for(int i = 0; i < 3; i++){
    printf("%s", line[i]);
  }
}

为什么在输入1来更改行后为什么打印出询问我要替换为什么的语句，并自动输入什么内容，然后将第一个字符串打印为空的语句自动显示?

Why is it that after I enter 1 to change the line, it prints the statement asking what I want to replace it with and will automatically enter nothing then printing the strings with the first one as empty?

我也已经尝试用 sscanf(％[^ \ n \ t] s"，line [0]); 读取该行，但是没有任何运气.有什么想法吗?

I also have already tried reading the line with sscanf("%[^\n\t]s", line[0]); without any luck. Any ideas?

推荐答案

是因为

scanf("%d",&option);

在stdin中保留 \ n 字符，并在第一次调用 fgets()时使用.这就是为什么最好完全避免在C语言中使用 scanf().

leaves the \n character in stdin and is consumed by the first call to fgets(). That's why it's best to avoid scanf() in C completely.

您可以使用以下方法修复它:

You can fix it with:

  scanf("%d",&option);
  getchar(); /* consume the newline */

但是我建议也使用 fgets()来读取 option ，然后您可以使用

But I'd suggest using fgets() to read option as well and then you can use strtol() to convert it into an integer.

请注意，此语句可能不是您想要的(这限制了您可以读入 line [0] 的内容).

Note that this statement is not probably what you intended (which limits what you can read into line[0]).

   fgets(line[0],strlen(line[0]),stdin);

您可能打算使用:

   fgets(line[0],sizeof line[0],stdin);

，以便您可以读取到 line [0] 的实际大小.

so that you can read upto the actual size of line[0].

请同时阅读C常见问题解答条目: http://c-faq.com/stdio/scanfprobs.html

Please read the C Faq entry as well: http://c-faq.com/stdio/scanfprobs.html

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