C++ Set value for a char**

问题:

I'm trying to assign a value to a char** variable. In my foo.h I've defined a couple of variables such as

#define APIOCTET         int
#define APILONG          long                  
#define APICHAR          char               
#define APISTRING        char* 

Now in my foo.cpp I'm tryng to use a method where

APILONG apiInitialize(APISTRING filePath, APISTRING* outputString)
{
  //open text file to where output will be printed
  //do other stuff, etc..
  //return result;
}

I'd like to assign a value to my APISTRING* outputString but I just can't figure out how to do so, I've tried many things which are basically a variation of the following code

APISTRING  error = "error";
APISTRING  other = "string";
APISTRING  charArr[] = { error, other, error };
APISTRING  *charArr2[] = { charArr };
errorString = *charArr2; 

Also im not 100% clear on what exactly is APISTRING* outputString. When I try to compile it gives me an error message where it mentions it's a char**. Is it a 2D array?.. A pointer to an array of chars?.. But most importantly, how would I assign a value for this variable? Thanks in advance.

回答1:

The APISTRING* is a pointer to a pointer to char. It holds an address which holds the address of the first character of the string in memory.

See this question for more info on double pointers in C/C++.

To assign to the string you would need to do *outputString = "string"

回答2:

APISTRING* outputString will be pre-processed and replcaed at compile-time as char** outputstring. Hence, outputString will be double pointer hence, you need to do it like this (below code). I combined both .h and cpp together for simplicity.

#include<iostream>
using namespace std;

#define APIOCTET         int
#define APILONG          long                  
#define APICHAR          char               
#define APISTRING        char* 

APILONG apiInitialize(APISTRING filePath, APISTRING* outputString)
{
    APISTRING getIt = *outputString;
    cout<<"  "<<getIt<<endl;
}

int main()
{
    APISTRING str = "hello";
    APISTRING* outputString = &str;
    APILONG val = apiInitialize("world", outputString );

    system("PAUSE");
    return 0;
}

I would recommend to use std::string, it'll be easy to tweak with certain behaviors. Hope this helps.