尝试将结构实例写入文件时遇到分段错误 [英] Getting a segmentation fault while trying to write a struct instance to a file

问题描述

我正在尝试将结构写入文件，但在运行时遇到分段错误:

I am trying to write a struct to a file, but am getting a segmentation fault at run time:

#include<stdio.h>

//just a struct for purposes of demonstration
struct my_struct{
  int prop1;
  int prop2;
};

//writes dummy struct to filename.dat
void writeStruct(){
  FILE *file_pointer;
  file_pointer = fopen("filename.dat","w");

  //define and assign variables to a quick dummy struct
  struct my_struct *this_struct;

  this_struct->prop1=0; //seg faults here!
  this_struct->prop2=1;

  //write struct to file
  fwrite(this_struct, sizeof(*this_struct), 1, file_pointer);

  fclose(file_pointer);

}

int main(){
  writeStruct();
  return 0;
}

有人可以帮助我了解seg错误并实现程序的目的吗?

Can anyone help me understand the seg fault and achieve the purpose of the program?

推荐答案

您仅定义了该结构的指针，未指向任何内存.所以只是不要使用指针:

You've only defined a pointer of the struct, not pointing to any memory. So just don't use a pointer:

...
  //define and assign variables to a quick dummy struct
  struct my_struct this_struct;

  this_struct.prop1=0;
  this_struct.prop2=1;

  //write struct to file
  fwrite(&this_struct, sizeof this_struct, 1, file_pointer);
...

或者因为想要那样使用malloc来分配内存:

Or since it's wanted that way use malloc to allocate the memory:

...
  //define and assign variables to a quick dummy struct
  struct my_struct *this_struct;

  this_struct = malloc(sizeof *this_struct);
  this_struct->prop1=0;
  this_struct->prop2=1;

  //write struct to file
  fwrite(this_struct, sizeof *this_struct, 1, file_pointer);
...

别忘了在指针无法到达之前调用free.

Don't forget to call free before the pointer goes out of reach.

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