C语言内存分配

[root@localhost Ctest]# ls test -l     //test为一个可执行程序
-rwxr-xr-x  1 root root 4868 Mar 26 08:10 test
[root@localhost Ctest]# file test //此文件基本情况
test: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 
for GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped
[root@localhost Ctest]# size test  //此二进制可执行文件结构情况
//代码区静态数据/全局初始化数据区　未初始化数据区　十进制总和　十六进制总和 文件名
text   data         bss    dec    hex filename
906    284          4    1194    4aa test

int   maxcount = 99;

static mincount=100;

long  sum[1000];

//main.cpp 
int a = 0;    //a在全局已初始化数据区 
char *p1;    //p1在BSS区（未初始化全局变量） 
main() 
{
int b;    //b在栈区
char s[] = "abc"; //s为数组变量，存储在栈区，
//"abc"为字符串常量，存储在已初始化数据区
char *p1，p2;  //p1、p2在栈区
char *p3 = "123456"; //123456在已初始化数据区，p3在栈区 
static int c =0；  //C为全局（静态）数据，存在于已初始化数据区
//另外，静态数据会自动初始化
p1 = (char *)malloc(10);//分配得来的10个字节的区域在堆区
p2 = (char *)malloc(20);//分配得来的20个字节的区域在堆区
free(p1);
free(p2);
} 

int a=100;

p1 = (char *)malloc(10*sizeof(int));//分配得来得10*4字节的区域在堆区

free(p1);

/* We don't have #include_next.   Define ANSI  for standard 32-bit words.  */
/* These assume 8-bit 'char's, 16-bit 'short int's,   and 32-bit 'int's and 'long int's.  */

/* Number of bits in a 'char'. */
#  define CHAR_BIT 8          //所占字节数
/* Minimum and maximum values a 'signed char' can hold.  */  //有符号字符型范围
#  define SCHAR_MIN (-128)
#  define SCHAR_MAX 127
/* Maximum value an 'unsigned char' can hold.  (Minimum is 0.)  */ //无符号字符型范围
#  define UCHAR_MAX 255
/* Minimum and maximum values a 'char' can hold.  */
#  ifdef __CHAR_UNSIGNED__
#   define CHAR_MIN 0
#   define CHAR_MAX UCHAR_MAX
#  else
#   define CHAR_MIN SCHAR_MIN
#   define CHAR_MAX SCHAR_MAX
#  endif

/* Minimum and maximum values a 'signed short int' can hold.  */ // 有符号短整型范围
#  define SHRT_MIN (-32768)
#  define SHRT_MAX 32767
/* Maximum value an 'unsigned short int' can hold.  (Minimum is 0.)  */// 无符号短整型范围
#  define USHRT_MAX 65535

/* Minimum and maximum values a 'signed int' can hold.  */  //整形范围
#  define INT_MIN (-INT_MAX - 1)     
#  define INT_MAX 2147483647
/* Maximum value an 'unsigned int' can hold.  (Minimum is 0.)  */ //无符号整形范围
#  define UINT_MAX 4294967295U

//come from /usr/include/bits/wordsize.h
#define __WORDSIZE 32

/* Minimum and maximum values a 'signed long int' can hold.  */ //有符号长整形范围
#  if __WORDSIZE == 64
#   define LONG_MAX 9223372036854775807L
#  else
#   define LONG_MAX 2147483647L
#  endif
#  define LONG_MIN (-LONG_MAX - 1L)
/* Maximum value an 'unsigned long int' can hold.  (Minimum is 0.)  *///无符号长整形范围
#  if __WORDSIZE == 64
#   define ULONG_MAX 18446744073709551615UL
#  else
#   define ULONG_MAX 4294967295UL
#  endif

#  ifdef __USE_ISOC99
/* Minimum and maximum values a 'signed long long int' can hold.  *///无符号长长整形范围
#   define LLONG_MAX 9223372036854775807LL
#   define LLONG_MIN (-LLONG_MAX - 1LL)
/* Maximum value an 'unsigned long long int' can hold.  (Minimum is 0.)  *///有符号长长整形范围
#   define ULLONG_MAX 18446744073709551615ULL
#  endif /* ISO C99 */

[root@localhost linux_app]# cat mem_add.c
#include 
#include 
#include 
#include 

extern void afunc(void);
extern etext,edata,end;

int bss_var;                                //未初始化全局数据存储在BSS区
int data_var=42;                            //初始化全局数据存储在数据区
#define SHW_ADR(ID,I) printf("the %8st is at adr:%8xn",ID,&I); //打印地址宏

int main(int argc,char *argv[])
{
char *p,*b,*nb;
printf("Adr etext:%8xt Adr edata %8xt Adr end %8xtn",&etext,&edata,&end);
printf("ntext Location:n");
SHW_ADR("main",main);              //查看代码段main函数位置
SHW_ADR("afunc",afunc);           //查看代码段afunc函数位置
printf("nbss Location:n");
SHW_ADR("bss_var",bss_var);      /查看BSS段变量位置
printf("ndata location:n");
SHW_ADR("data_var",data_var);     /查看数据段变量
printf("nStack Locations:n"); 
afunc();
p=(char *)alloca(32);              //从栈中分配空间
if(p!=NULL)
{
SHW_ADR("start",p);
SHW_ADR("end",p+31);
}
b=(char *)malloc(32*sizeof(char));   //从堆中分配空间
nb=(char *)malloc(16*sizeof(char));  //从堆中分配空间
printf("nHeap Locations:n");
printf("the Heap start: %pn",b);   //堆起始位置
printf("the Heap end:%pn",(nb+16*sizeof(char)));//堆结束位置
printf("nb and nb in Stackn");
SHW_ADR("b",b);       //显示栈中数据b的位置
SHW_ADR("nb",nb);       //显示栈中数据nb的位置
free(b);         //释放申请的空间，以避免内存泄漏
free(nb);         //释放申请的空间，以避免内存泄漏
}

void afunc(void)
{
static int long level=0;          //静态数据存储在数据段中
int      stack_var;                 //局部变量，存储在栈区
if(++level==5)
{
return;
}
printf("stack_var is at:%pn",&stack_var);
//      SHW_ADR("stack_var in stack section",stack_var);
//      SHW_ADR("Level in data section",level);
afunc();
}

[root@localhost linux_app]# gcc -o mem_add mem_add.c //编译
[root@localhost linux_app]# ./mem_add     //运行结果
Adr etext: 8048702       Adr edata  8049950      Adr end  804995c

text Location:
the     main     is at adr: 8048418
the    afunc     is at adr: 8048611

bss Location:
the  bss_var     is at adr: 8049958

data location:
the data_var     is at adr: 804994c

Stack Locations:
the stack_var in stack section    is at adr:bfbf6c44
the Level in data section         is at adr: 8049954
the stack_var in stack section    is at adr:bfbf6c24
the Level in data section         is at adr: 8049954
the stack_var in stack section    is at adr:bfbf6c04
the Level in data section         is at adr: 8049954
the stack_var in stack section    is at adr:bfbf6be4
the Level in data section         is at adr: 8049954
the    start     is at adr:bfbf6c74
the      end     is at adr:bfbf6cf0

Heap Locations:
the Heap start: 0x8453008
the Heap end:0x8453040

b and nb in Stack
the        b     is at adr:bfbf6c70
the       nb     is at adr:bfbf6c6c

[root@localhost yangzongde]# readelf -a memadd

＃include

void *malloc(size_t　size)   //返回类型为空指针类型
void free(void *ptr)

int *p1,*p2;
p1=(int *)malloc(10*sizeof(int));
p2=p1;
……
free(p2) ;      /*或者free(p1)*/ 
p1=NULL;       /*或者p2=NULL */

[root@localhost yangzongde]# cat malloc_example.c 
#include               //printf()    //(1)头文件信息
#include              //malloc()    //(2)
int main(int argc,char* argv[],char* envp[])   //(3)
{
int count;
int* array; 
if((array=(int *)malloc(10*sizeof(int)))==NULL)  //(4)分配空间
{
printf("malloc memory unsuccessful");
exit(1);
}
for (count=0;count<10;count++)      //(5) 赋值
{
*array=count;
array++;
}
for(count=9;count>=0;count--)                  //(6)赋值
{
array--;
printf("%4d",*array);
}
printf("n");
free(array);        //(7)释放空间
array=NULL;       //(8)将指针置为空，避免不安全访问
exit (0);
} 
[root@localhost yangzongde]# gcc -o malloc_example malloc_example.c  //编译
[root@localhost yangzongde]# ./malloc_example       //运行
9   8   7   6   5   4   3   2   1   0

static void* operator new(size_t sz);     //new运算符
static void  operator delete(void* p);      //delete运算符

void UseNewDelete(void)
{
Obj  *a = new Obj;           //申请动态内存并且初始化
//…
delete a;                   //清除并且释放内存
}

class A
{
public:
A()  {   cout<<"A is here!"<<ENDL;&NBSP;&NBSP; 构造函数
～A() {   cout<<"A is dead!"<<ENDL;&NBSP;&NBSP; }  ="" 析构函数
private:
int i;
};
A* pA=new A;     //调用new运算符申请空间
delete pA;      //删除pA 

void *realloc(void *ptr,size_t size)

＃include<stdlib.h>

ptr=realloc(ptr,new_amount)

[root@localhost yangzongde]# cat realloc_example.c 
#include <stdio.h>
#include <stdlib.h>
int main (int argc,char* argv[],char* envp[])   //(1)主函数
{
int input;
int n;
int *numbers1;
int *numbers2;
numbers1=NULL;

     if((numbers2=(int *)malloc(5*sizeof(int)))==NULL) //(2)numbers2指针申请空间
{
printf("malloc memory unsuccessful");
//free(numbers2);
numbers2=NULL;
exit(1);
}
for (n=0;n<5;n++)       //(3)初始化
{
*(numbers2+n)=n;
printf("numbers2's data: %dn",*(numbers2+n));
}

     printf("Enter an integer value you want to remalloc ( enter 0 to stop)n");//(4)新申请空间大小　
scanf ("%d",&input);

numbers1=(int *)realloc(numbers2,(input+5)*sizeof(int));  //(5)重新申请空间
if (numbers1==NULL) 
{ 
printf("Error (re)allocating memory"); 
exit (1); 
}

     for(n=0;n<5;n++)       //(6)这5个数是从numbers2拷贝而来
{
printf("the numbers1s's data copy from numbers2: %dn",*(numbers1+n));
}

     for(n=0;n<input;n++)       //(7)新数据初始化
{
*(numbers1+5+n)=n*2;
printf ("nummber1's new data: %dn",*(numbers1+5+n)); // numbers1++;
}
printf("n");
free(numbers1);       //(8)释放numbers1
numbers1=NULL;
// free(numbers2);     //(9)不能再释放numbers2
return 0;
} 
[root@localhost yangzongde]# gcc -o realloc_example realloc_example.c 
[root@localhost yangzongde]# ./realloc_example 
numbers2's data: 0
numbers2's data: 1
numbers2's data: 2
numbers2's data: 3
numbers2's data: 4
Enter an integer value you want to remalloc ( enter 0 to stop) //重新申请空间
5  
the numbers1s's data copy from numbers2: 0
the numbers1s's data copy from numbers2: 1
the numbers1s's data copy from numbers2: 2
the numbers1s's data copy from numbers2: 3
the numbers1s's data copy from numbers2: 4
nummber1's new data: 0
nummber1's new data: 2
nummber1's new data: 4
nummber1's new data: 6
nummber1's new data: 8

ptr=(struct data *)calloc (count,sizeof(strunt data)) //申请并初始化空间

void *calloc(size_t nmemb,size_t size)
{
void *p;
size_t total;
total=nmemb *size;
p=malloc(total);         //申请空间
if(p!=NULL)
memset(p,'',total);      //将其实始化为
return p;
}

/* Allocate a block that will be freed when the calling function exits.  */
extern void *alloca (size_t __size) __THROW;   //从栈中申请空间