Question

我是一个C ++新手，我试图用字符串练习指针。我所做的程序只是存储用户在命令行中键入的字符串。但是我得到了段错，不知道为什么。

这是代码：

#include <cstdio>
#include <cstdlib>
#include <iostream>

using namespace std;

//This code is meant to learn how to use pointers and strings
//Ask the user for who are they in the family and save it in string array!


void print_string (string* Value, int const nSize);
int get_names(string* Family_input);

int main ( int nNumberofArgs, char* pszArgs[])
{

  cout << "Tis program stores your family members\n";
  cout<< "Type the names and write 0 to exit\n";

  string familia_string;
  string* familia = &familia_string;

  int family_number;

  family_number=get_names(familia);  

  cout << "The family members are: ";  

  print_string(familia, family_number);

  cout << endl;

  return 0;
}

int get_names(string* Family_input)
{
  int i=0;
  string input="";
  string old_input="";
  while (input!="0")
  {
    cout << "type " << i <<" member\n";
    //cin >> *(Family_input+i);
    //input=*(Family_input+i);
    cin >> input;
    *(Family_input + old_input.length()) = input;
    old_input=input;
    i++;
  }
  return i;

}

void print_string (string* Value, int const nSize)
{// I don't want to &psValue to be changed!
  for (int i=0; i<nSize; i++)
  {
     cout << *(Value+i) << " ";
     //&psValue++;
  }
}

我不确定是不是因为我没有正确使用字符串的大小，或者我没有正确使用指针，或者我必须分配内存在使用偏移之前。

Answer 1

正如@kleszcz已指出的那样，行

*(Family_input + old_input.length()) = input;

错了。您正在访问您不应该访问的内存。

最简单的解决方法是稍微更改get_names：

int get_names(string* Family_input)
{
   int i=0;
   string input="";
   while (input!="0")
   {
      cout << "type " << i <<" member\n";
      cin >> input;
      *Family_input += input; // Just keep on appending to the input argument.
      *Family_input += "\n"; // Add a newline to separate the inputs.
      i++;
   }
   return i;
}

同时将print_string更改为：

void print_string (string* Value)
{
   cout << *Value;
}

当然，print_string变得如此简单，你根本不需要它。

您可以更改get_names以使用引用参数而不是指针参数。这是一种更好的做法。

int get_names(string& Family_input)
{
   int i=0;
   string input="";
   while (input!="0")
   {
      cout << "type " << i <<" member\n";
      cin >> input;
      Family_input += input; // Just keep on appending to the input argument.
      Family_input += "\n"; // Add a newline to separate the inputs.
      i++;
   }
   return i;
}

然后，将呼叫更改为get_names。而不是使用

family_number=get_names(familia);

使用

family_number=get_names(familia_string);

Answer 2

你得到seg错误，因为你没有为一个字符串数组分配内存。

*(Family_input + old_input.length()) = input;

这完全是胡说八道。如果你有一个数组，你只需将索引增加一个而不是字符串长度。

Answer 3

如果你想在不同的字符串对象中保存不同的名字，我建议：

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

void print_string(string** Value, int const nSize);
void get_names(string** Family_input, int count);


int main(int nNumberofArgs, char* pszArgs[]) {

cout << "This program stores your family members\n";
int family_number;
cout << "Types the number of family members";
cin >> family_number;

/*allocate the number of string pointers that you need*/
string** familia = new string*[family_number];

cout << "Type the names\n";

get_names(familia, family_number);

cout << "The family members are: ";

print_string(familia, family_number);

cout << endl;

return 0;
}

void get_names(string** Family_input, int count) {

for(int i = 0 ; i < count; i++){
    cout << "type " << i << " member\n";
    /*create a string obj in the heap memory*/
    string *input = new string ("");
    // using that way you get only a single word
    cin >> *input;
    /*create a string object on the stack and put its pointer in the family_array*/
    Family_input[i] = input;
}
}

void print_string(string** Value, int const nSize) {
for (int i = 0; i < nSize; i++) {
    cout << *(Value[i]) << " ";
}
}

使用字符串指针进行分段错误

3 个答案: