编译器不喜欢void：'（ - 函数声明

Question

I am trying to write a function to change some folder names, but I am having difficulties in the actual declaration.

Here is my code:

void ChangeVersion(char* NewVer)
{
    ifstream show_current_version;
    show_current_version.open(*removed*);
    char show_current_version_var[1024];
    if (show_current_version.is_open())
    {
        while (!show_current_version.eof())
        {
              show_current_version >> show_current_version_var;
        }                                         
    }
    show_current_version.close();
    // show_current_version_var is old version
    char OldVersion[1024] = show_current_version_var;

    // start rename
    cout << "Changing versions...";
    rename("*removed*", OldVersion);
    rename(NewVer, "*removed*");
    cout << "done!" << endl; 
} 

As you can tell, I am new to c++...

I have read on various c++ tutorial websites, that if you want a function to not return anything, then you declare it as void. However when I did this, my compiler says invalid initializer. I am using dev-cpp.

I am thinking it is because my function is outputting text, but on the websites, the void function has some cout statements...

I have tried initializing it with char*, like my other functions, yet I get the same error. Same with int and char.

Thank you for reading.

Answer 1

You really should give the output of the compiler a closer look. It generally tells you what line contains the error, which gives you a lot to work with.

Getting to the particular problem the offending line (from what I gather, havent tried compiling) is:

char OldVersion[1024] = show_current_version_var;

You can't assign a variable to a static array like that. There's only a handful of things one can use to initialize a static array. For example:

char OldVersion[1024] = "Static string";
char example[1024] = { 0 };

Try doing:

char OldVersion[1024];
strncpy(OldVersion, show_current_version_var, 1024);
// Null-terminate the string for good measure
OldVersion[1023] = 0;

Or simply use show_current_version_var where you would use OldVersion (I see no reason to copy the string in the code you pasted).

Anyway, I don't know what you're trying to accomplish, but you really should read up on C++. It's a rather tricky language to use.

Answer 2

Couple of small things

When you post code, post everything that we need to compile it:

// You need these to make it compile.
#include <iostream>
#include <fstream>

using namespace std;

OK. Bugs:

show_current_version.open(*removed*);
                          ^^^^^^^^^   What is this supposed to be ?

This function is expecting a C-String. So "removed" is valid. But the stars * don't make sense.

char OldVersion[1024] = show_current_version_var;

You can't copy arrays like that:

char OldVersion[1024];
std::copy(show_current_version_var, show_current_version_var+1024, OldVersion);

What would be better though is to use std::vector rather than an array. Then you are allowed to copy.

std::vector<char>   show_current_version_var(1024);
// STUFF
std::vector<char>   OldVersion(show_current_version_var);

Alternatively if you are specifically storing strings (not blobs of char) then std::string is probably your best bet.

Answer 3

I don't think that you can do this:

char OldVersion[1024] = show_current_version_var;

You can only initialise arrays with a brace-list (like {'p', 'a', 'x'} for example).

Instead, you should try:

char OldVersion[1024];
memcpy (OldVersion, show_current_version_var, sizeof (OldVersion));

A complete, compilable version is shown below:

#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
void ChangeVersion(char* NewVer)
{
    ifstream show_current_version;
    show_current_version.open("qqq");
    char show_current_version_var[1024];
    if (show_current_version.is_open())
    {
        while (!show_current_version.eof())
        {
              show_current_version >> show_current_version_var;
        }
    }
    show_current_version.close();
    // show_current_version_var is old version
    char OldVersion[1024];
    memcpy (OldVersion, show_current_version_var, sizeof (OldVersion));

    // start rename
    cout << "Changing versions...";
    rename("*removed*", OldVersion);
    rename(NewVer, "*removed*");
    cout << "done!" << endl;
}

int main() {
    return 0;
}