Invalid Initializer When I try to call function from another function-CodePudding

I have two functions. One that returns the part of the string for me. Don't ask me why I'm doing it inside a function because I want to run this inside a thread.

When I try to get the return value from another function that will return and store it inside a variable an error occur. It says Invalid initializer.

Long time no coding with C programming language. So I'm sorry if there are some basic mistakes.

Can anyone help with this problem?

My code goes like below:

void *encrypt(char data[])
{
     //code goes here
    return data[];
}

void *firstThread(void *message)
{
    code goes here
    .
    .
    .
    char message[40] = encrypt(data);//returns Invalid Inıtıalızer
}

CodePudding user response：

The both functions are invalid.

In the first function the return expression is wrong

return data[];

You have to write

return data;

The compiler adjusts the function parameter having the array type to pointer to the array element type like

void *encrypt(char *data);

This pointer is returned from the function casted to the type void *.

In the second function you are trying to initialize an array with a pointer of the type void *

char message[40] = encrypt(data);//returns Invalid Inıtıalızer

You may not do that. Instead you could write for example

#include <string.h>

//...

void *firstThread(void *message)
{
    code goes here
    .
    .
    .
    char message[40];

    strcpy( message, encrypt(data) );
}

provided that the returned pointer from the function encript points to a string. Otherwise you need to supply some way also the size of the pointed array to use the function memcpy instead of strcpy.

Or you could just declare within the function firstThread a pointer provided that the pointed array will be still alive

void *firstThread(void *message)
{
    code goes here
    .
    .
    .
    char *message = encrypt(data);
}

CodePudding user response：

You cannot assign pointers to arrays!

If you want to initialise arrays you need to provide an appropriate initialiser like:

char message[40] = { 1, 2, 3 /* rest will be 0 };

If you want the array to contain data you receive via some pointer you need to explicitly copy it:

char message[40];
memcpy(message, encrypt(data), 0);

Well, in above statement nothing will be copied. Instead of 0 you need to provide the minimum of message's size and the size of the data returned by your function.

Apart from you have a duplicate variable name: message as parameter and message as local variable.