C - memset segfault for statically allocated char array

Question

I get a segfault when trying to memset an array of chars that was allocated statically, but not for an array of the same length that was allocated using malloc .

variable definitions:

    //static
    char inBuff[IN_BUFF_LEN];
    //dynamic
    char * inBuffD;

function call:

    //static, cast used because char** != char (*) [n]
    serverInit(portNum, (char**) &inBuff, &serv_addr, &sockfd)
    //dynamic
    serverInit(portNum, &inBuffD, &serv_addr, &sockfd)

use within the function:

    memset(*inBuffAdr, 0, IN_BUFF_LEN);

I suspect that my problem is in the difference of the function calls, or to be more precise, my incomplete understanding of the "char** != char (*) [n]" situation. But I have been banging at this for too long and can't see the forest from the trees so any hints and advice would be very appreciated.

Answer 1

只需发送inBuff（不是** inBuff），然后发送memset inBuffAdr而不是* inBufAdr（您的其他memset可能也不起作用，您只是还不知道）

Answer 2

Why do you need to pass a double-pointer to your serverInit() function? If the function can modify where the pointer points to, then you can't pass a statically allocated array. If the function can't modify where the pointer points to, then you don't need a double-pointer.

The type of &inBuff is pointer to array of char of size IN_BUFF_LEN , which is quite distinct from a char ** . You've bludgeoned the compiler into not complaining, claiming that you know better than the compiler what you're doing. Don't use a cast like that unless you are sure you do know more than the compiler.

Frankly, given the current prototype, you'd probably be best off with:

//static
char inBuff[IN_BUFF_LEN];
char *inBuffS = inBuff;
//dynamic
char *inBuffD;

serverInit(portNum, &inBuffS, &serv_addr, &sockfd);

However, I'm deeply suspicious that you should revise serverInit() to take a simple char * instead of char ** for the second argument.

Answer 3

Why not define serverInit() the following way:

serverInit(...., char * inBuff, ....)

then call it

serverInit(...., inBuff, ....)

and then inside serverInit() call memset() like this:

memset(inBuff, 0, IN_BUFF_LEN);

Answer 4

Part of your confusion is in thinking that &inBuff can be dereferenced to get inBuff . If you run this simple test program:

#include <stdio.h>
char inBuff[1000];
int main( int argc, char *argv[])
{
    printf( "%p %p\n", inBuff, &inBuff);
    return 0;
}

You'll see that it prints the same address for both notations. If you try to dereference &inBuff , you'll be taking the first few bytes of the array as an address.

As others have stated, you should just be passing a pointer to the memory you're going to set. Hopefully this answer will help you with future debugging sessions.