Malloc中的编译错误

Question

I'm following this tutorial to write my own version of malloc and free. The full source code is here which I'm trying to run on my laptop.

I have 3 files:

mymalloc.h
mymalloc.c
memgrind.c // Where my main method is to test my malloc function

I try to compile it by executing the following on the command line:

gcc -c mymalloc.c
gcc -o memgrind.c memgrind

But I get the following errors:

warning: implicit declaration of function MyMalloc [-Wimplicit-function-declaration]
 int *p=(int)MyMalloc(100*sizeof(int));
             ^~~~~~~~
memgrind.c:5:8: warning: initialization makes pointer from integer without a cast [-Wint-conversion]
 int *p=(int)MyMalloc(100*sizeof(int));

Am I compiling my files wrong? Or something wrong with the code? (The code I'm executing & compiling is no different to the source code provided in the link)

Thank you.

EDIT:

Now it is compiling correctly but I get this error:

/tmp/ccKyTOaY.o:(.data.rel.local+0x0): multiple definition of `freeList'
/tmp/cc0jpDeq.o:(.data.rel.local+0x0): first defined here
collect2: error: ld returned 1 exit status

But I'm only declaring it once inside of my mymalloc.h?

For reference, here is the code:

mymalloc.c

#include<stdio.h>
#include<stddef.h>
#include "mymalloc.h"


void initialize(){
 freeList->size=20000-sizeof(struct block);
 freeList->free=1;
 freeList->next=NULL;
}

void split(struct block *fitting_slot,size_t size){
 struct block *new=(void*)((void*)fitting_slot+size+sizeof(struct block));
 new->size=(fitting_slot->size)-size-sizeof(struct block);
 new->free=1;
 new->next=fitting_slot->next;
 fitting_slot->size=size;
 fitting_slot->free=0;
 fitting_slot->next=new;
}


void *MyMalloc(size_t noOfBytes){
 struct block *curr,*prev;
 void *result;
 if(!(freeList->size)){
  initialize();
  printf("Memory initialized\n");
 }
 curr=freeList;
 while((((curr->size)<noOfBytes)||((curr->free)==0))&&(curr->next!=NULL)){
  prev=curr;
  curr=curr->next;
  printf("One block checked\n");
 }
 if((curr->size)==noOfBytes){
  curr->free=0;
  result=(void*)(++curr);
  printf("Exact fitting block allocated\n");
  return result;
 }
 else if((curr->size)>(noOfBytes+sizeof(struct block))){
  split(curr,noOfBytes);
  result=(void*)(++curr);
  printf("Fitting block allocated with a split\n");
  return result;
 }
 else{
  result=NULL;
  printf("Sorry. No sufficient memory to allocate\n");
  return result;
 }
}

void merge(){
 struct block *curr,*prev;
 curr=freeList;
 while((curr->next)!=NULL){
  if((curr->free) && (curr->next->free)){
   curr->size+=(curr->next->size)+sizeof(struct block);
   curr->next=curr->next->next;
  }
  prev=curr;
  curr=curr->next;
 }
}

void MyFree(void* ptr){
 if(((void*)memory<=ptr)&&(ptr<=(void*)(memory+20000))){
  struct block* curr=ptr;
  --curr;
  curr->free=1;
  merge();
 }
 else printf("Please provide a valid pointer allocated by MyMalloc\n");
}

mymalloc.h

#include<stdio.h>
#include<stddef.h>

char memory[20000];

struct block{
 size_t size;
 int free;
 struct block *next; 
};

struct block *freeList=(void*)memory;

void initialize();
void split(struct block *fitting_slot,size_t size);
void *MyMalloc(size_t noOfBytes);
void merge();
void MyFree(void* ptr);

memgrind.c

#include<stdio.h>
#include "mymalloc.h"

int main(){
 
 int *p=(int*)MyMalloc(100*sizeof(int));
 char *q=(char*)MyMalloc(250*sizeof(char));
 int *r=(int*)MyMalloc(1000*sizeof(int));
 MyFree(p);
 char *w=(char*)MyMalloc(700);
 MyFree(r);
 int *k=(int*)MyMalloc(500*sizeof(int));
 printf("Allocation and deallocation is done successfully!");
}

Answer 1

警告说你试图把int放入int *所以试试这个

int *p=(int*)MyMalloc(100*sizeof(int));