为什么 scanf 扫描空值 [英] why scanf scans a null value

问题描述

在下面的代码中:

#include <stdio.h>

int main(){

  char *name;
  int age;  
  char *gen;

  printf("Your name:");
  scanf("%s",name);

  printf("Your age:");
  scanf("%d",&age);

  printf("Your gender:");
  scanf("%s",gen);

  printf("*****************\n");

  printf("%s is a %d years old %s \n",name,age,gen);

  return 0;  

}

当我这样运行时:

Your name:tom
Your age:20
Your gender:male
*****************
tom is a 20 years old (null)

如你所见，gen 是一个空值，为什么 scanf 读入 gen 失败，但前两次读取成功?

As you can see, gen is a null value, Why scanf fails reading into gen but the first two readings success?

推荐答案

char *name;
char *gen;

只是字符指针，什么也不指向.所以需要为它分配内存.

are just char pointer and point nothing. So need to allocate memory for it.

你可以为它分配内存

char *name = malloc(100);
char *gen  = malloc(100);

OR 定义具有预定义长度的字符数组

OR define char array with predefined length

char name[100];
char gen[100];

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