C++ C/C++；argv内存管理
一种标准的C/C++程序格式C++ C/C++；argv内存管理,c++,c,memory-management,C++,C,Memory Management,一种标准的C/C++程序格式 int main(int argc, char *argv[]){} 我想知道调用main时，argv数据在内存中是如何排列的。我从Node.js repo获得了这个函数。它的工作原理就像内存是这样排列的： argv_area|NULL|argv_data_area 操作系统真的以这种方式处理argv的内存吗 就操作系统依赖性而言，只需讨论Linux 64位您在Node.js中链接的代码实际上并不假设任何关于argv及其引用的布局。相反，您提到的布局是函数的输出
int main(int argc, char *argv[]){}
mainargvargv_area|NULL|argv_data_area
就操作系统依赖性而言，只需讨论Linux 64位您在Node.js中链接的代码实际上并不假设任何关于argv及其引用的布局。相反，您提到的布局是函数的输出格式。事实上，它确实像您所说的那样创建了一个数组，但它不需要像这样排列输入（如果这样做了，它可以只执行一个
memcpy（） // Logic to duplicate argv as Init() modifies arguments
// that are passed into it.
char **argv_copy = copy_argv(argc, argv);
// This needs to run *before* V8::Initialize()
// Use copy here as to not modify the original argv:
Init(argc, argv_copy);
为什么会这样？因为
Init（）。对我来说，这似乎有点迂回，但您发现的argv复制例程的全部目的只是为了让程序能够使用它作为argv，而不是对它们使用的确切布局有任何特定的要求。不过它是一个简单的布局，以后只需要一个free（）
。原始的argv
通常作为单个连续的char*
值块处理，紧接着是环境的另一个char*
值块（int main中的envp
）（int-argc，char**argv，char**envp）
是main（）
的变体，也是由environ
指向的）。然后是参数字符串和环境字符串本身
参数列表和环境可能不是由malloc（）
本身创建的-参数和环境是通过execve（）
系统调用设置的
三年前的某个时候，我在玩“从main以外的函数中查找argv[0]
”，并编写了如下代码。它仍然适用于Mac OS X Mavericks（10.9.4-最初测试的版本是Snow Leopard 10.6）和Ubuntu14.04。（有更好的、但特定于平台的方法来获取argv[0]
来自一个函数，但这是一个函数，因此我不会使用此技术，但它在一些常见平台上确实有效。）
#包括“posixver.h”
#包括
#包括
#包括
#include/*putenv（），setenv（）*/
外部字符**environ；/*应在中声明*/
/*
**练习的目的是：只考虑环境（因为这就是全部）
**可用于库函数）尝试查找argv[0]（和
**因此，argc）。
**
**在某些平台上，内存的布局使得
**参数（argc）可用，后跟参数向量，
**其次是环境向量。
**
**argv环境
** | |
**v v
**| argc | argv0 | argv1 | | | argvN | 0 | env0 | env1 | | envN | 0|
**
**这适用于：
**--Solaris 10（32位、64位SPARC）
**--MacOS X 10.6（雪豹、32位和64位）
**--Linux（x86/64、32位和64位上的RHEL 5）
**
**遗憾的是，在另外两个Unix系统上，情况并非如此
**平台。argv0前面的值似乎是0。
**--AIX 6.1（32位、64位）
**--HP-UX 11.23 IA64（32位，64位）
**次标准POSIX支持（无setenv（））和C99支持（无%zd）。
**
**注意：如果调用putenv（）或setenv（）来添加环境变量，
**然后environ的基址发生了根本性的变化，从
**堆叠到堆上，所有下注均已取消。修改现有
**变量不是问题。
**
**通过观察是否
**environ指向的地址是大小的128k倍以上
**来自局部变量地址的指针。
**
**这段代码名义上是难以置信的特定于机器的，但实际上是
**非常便于携带。
*/
typedef结构参数
{
字符**argv；
尺寸参数；
}争论；
静态无效打印\u cpp（常量字符*标记，整数i，字符**ptr）
{
uintptr_t p=（uintptr_t）ptr；
printf（“%s[%d]=0x%PRIXPTR”（0x%PRIXPTR）（%s）\n”，
标签，i，p，（uintptr_t）（*ptr），（*ptr==0？”：*ptr））；
}
枚举{MAX_DELTA=sizeof（void*）*128*1024}；
静态参数find_argv0（void）
{
静态字符*dummy[]={'，0}；
参数args；
uintptruêt i；
字符**基=环境-1；
uintpttr_t delta=（（uintpttr_t）和base>（uintpttr_t）environment）？（uintpttr_t）和base-（uintpttr_t）environment:（uintpttr_t）environment-（uintpttr_t）和base；
如果（增量<最大值_增量）
{
对于（i=2；（uintptr\u t）（*（环境-i）+2）！=i&（uintptr\u t）（*（环境-i））！=0；i++）
打印cpp（“测试”，i，环境-i）；
args.argc=i-2；
args.argv=environ-i+1；
}
其他的
{
args.argc=1；
args.argv=虚拟；
}
printf（“argc=%zd\n”，args.argc）；
对于（i=0；i环境）？argv-environ:environ-argv；
printf（“环境=0x%lX；argv=0x%lX（增量：0x%lX）\n”，（无符号长）环境，（无符号长）argv，增量）；
对于（i=0；i（无符号长）argc+1）
返回0；
对于（i=1；i#include "posixver.h"
#include <inttypes.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h> /* putenv(), setenv() */
extern char **environ; /* Should be declared in <unistd.h> */
/*
** The object of the exercise is: given just environ (since that is all
** that is available to a library function) attempt to find argv[0] (and
** hence argc).
**
** On some platforms, the layout of memory is such that the number of
** arguments (argc) is available, followed by the argument vector,
** followed by the environment vector.
**
** argv environ
** | |
** v v
** | argc | argv0 | argv1 | ... | argvN | 0 | env0 | env1 | ... | envN | 0 |
**
** This applies to:
** -- Solaris 10 (32-bit, 64-bit SPARC)
** -- MacOS X 10.6 (Snow Leopard, 32-bit and 64-bit)
** -- Linux (RHEL 5 on x86/64, 32-bit and 64-bit)
**
** Sadly, this is not quite what happens on the other two Unix
** platforms. The value preceding argv0 seems to be a 0.
** -- AIX 6.1 (32-bit, 64-bit)
** -- HP-UX 11.23 IA64 (32-bit, 64-bit)
** Sub-standard POSIX support (no setenv()) and C99 support (no %zd).
**
** NB: If putenv() or setenv() is called to add an environment variable,
** then the base address of environ changes radically, moving off the
** stack onto heap, and all bets are off. Modifying an existing
** variable is not a problem.
**
** Spotting the change from stack to heap is done by observing whether
** the address pointed to by environ is more than 128 K times the size
** of a pointer from the address of a local variable.
**
** This code is nominally incredibly machine-specific - but actually
** works remarkably portably.
*/
typedef struct Arguments
{
char **argv;
size_t argc;
} Arguments;
static void print_cpp(const char *tag, int i, char **ptr)
{
uintptr_t p = (uintptr_t)ptr;
printf("%s[%d] = 0x%" PRIXPTR " (0x%" PRIXPTR ") (%s)\n",
tag, i, p, (uintptr_t)(*ptr), (*ptr == 0 ? "<null>" : *ptr));
}
enum { MAX_DELTA = sizeof(void *) * 128 * 1024 };
static Arguments find_argv0(void)
{
static char *dummy[] = { "<unknown>", 0 };
Arguments args;
uintptr_t i;
char **base = environ - 1;
uintptr_t delta = ((uintptr_t)&base > (uintptr_t)environ) ? (uintptr_t)&base - (uintptr_t)environ : (uintptr_t)environ - (uintptr_t)&base;
if (delta < MAX_DELTA)
{
for (i = 2; (uintptr_t)(*(environ - i) + 2) != i && (uintptr_t)(*(environ - i)) != 0; i++)
print_cpp("test", i, environ-i);
args.argc = i - 2;
args.argv = environ - i + 1;
}
else
{
args.argc = 1;
args.argv = dummy;
}
printf("argc = %zd\n", args.argc);
for (i = 0; i <= args.argc; i++)
print_cpp("argv", i, &args.argv[i]);
return args;
}
static void print_arguments(void)
{
Arguments args = find_argv0();
printf("Command name and arguments\n");
printf("argc = %zd\n", args.argc);
for (size_t i = 0; i <= args.argc; i++)
printf("argv[%zd] = %s\n", i, (args.argv[i] ? args.argv[i] : "<null>"));
}
static int check_environ(int argc, char **argv)
{
size_t n = argc;
size_t i;
unsigned long delta = (argv > environ) ? argv - environ : environ - argv;
printf("environ = 0x%lX; argv = 0x%lX (delta: 0x%lX)\n", (unsigned long)environ, (unsigned long)argv, delta);
for (i = 0; i <= n; i++)
print_cpp("chkv", i, &argv[i]);
if (delta > (unsigned long)argc + 1)
return 0;
for (i = 1; i < n + 2; i++)
{
printf("chkr[%zd] = 0x%lX (0x%lX) (%s)\n", i, (unsigned long)(environ - i), (unsigned long)(*(environ - i)),
(*(environ-i) ? *(environ-i) : "<null>"));
fflush(0);
}
i = n + 2;
printf("chkF[%zd] = 0x%lX (0x%lX)\n", i, (unsigned long)(environ - i), (unsigned long)(*(environ - i)));
i = n + 3;
printf("chkF[%zd] = 0x%lX (0x%lX)\n", i, (unsigned long)(environ - i), (unsigned long)(*(environ - i)));
return 1;
}
int main(int argc, char **argv)
{
printf("Before setting environment\n");
if (check_environ(argc, argv))
print_arguments();
//putenv("TZ=US/Pacific");
setenv("SHELL", "/bin/csh", 1);
printf("After modifying environment\n");
if (check_environ(argc, argv) == 0)
printf("Modifying environment messed everything up\n");
print_arguments();
putenv("CODSWALLOP=nonsense");
printf("After adding to environment\n");
if (check_environ(argc, argv) == 0)
printf("Adding environment messed everything up\n");
print_arguments();
return 0;
}
Before setting environment
environ = 0x7FFF584D04C8; argv = 0x7FFF584D0498 (delta: 0x6)
chkv[0] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
chkv[1] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
chkv[2] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
chkv[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
chkv[4] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
chkv[5] = 0x7FFF584D04C0 (0x0) (<null>)
chkr[1] = 0x7FFF584D04C0 (0x0) (<null>)
chkr[2] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
chkr[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
chkr[4] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
chkr[5] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
chkr[6] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
chkF[7] = 0x7FFF584D0490 (0x5)
chkF[8] = 0x7FFF584D0488 (0x0)
test[2] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
test[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
test[4] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
test[5] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
test[6] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
argc = 5
argv[0] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
argv[1] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
argv[2] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
argv[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
argv[4] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
argv[5] = 0x7FFF584D04C0 (0x0) (<null>)
Command name and arguments
argc = 5
argv[0] = ./find_argv0
argv[1] = macedonian
argv[2] = obelisk
argv[3] = mental breakdown
argv[4] = testing: 1, 2, 3
argv[5] = <null>
After modifying environment
environ = 0x7FFF584D04C8; argv = 0x7FFF584D0498 (delta: 0x6)
chkv[0] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
chkv[1] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
chkv[2] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
chkv[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
chkv[4] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
chkv[5] = 0x7FFF584D04C0 (0x0) (<null>)
chkr[1] = 0x7FFF584D04C0 (0x0) (<null>)
chkr[2] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
chkr[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
chkr[4] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
chkr[5] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
chkr[6] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
chkF[7] = 0x7FFF584D0490 (0x5)
chkF[8] = 0x7FFF584D0488 (0x0)
test[2] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
test[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
test[4] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
test[5] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
test[6] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
argc = 5
argv[0] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
argv[1] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
argv[2] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
argv[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
argv[4] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
argv[5] = 0x7FFF584D04C0 (0x0) (<null>)
Command name and arguments
argc = 5
argv[0] = ./find_argv0
argv[1] = macedonian
argv[2] = obelisk
argv[3] = mental breakdown
argv[4] = testing: 1, 2, 3
argv[5] = <null>
After adding to environment
environ = 0x7FB1EA403B60; argv = 0x7FFF584D0498 (delta: 0x9ADC19927)
chkv[0] = 0x7FFF584D0498 (0x7FFF584D06B0) (./find_argv0)
chkv[1] = 0x7FFF584D04A0 (0x7FFF584D06BD) (macedonian)
chkv[2] = 0x7FFF584D04A8 (0x7FFF584D06C8) (obelisk)
chkv[3] = 0x7FFF584D04B0 (0x7FFF584D06D0) (mental breakdown)
chkv[4] = 0x7FFF584D04B8 (0x7FFF584D06E1) (testing: 1, 2, 3)
chkv[5] = 0x7FFF584D04C0 (0x0) (<null>)
Adding environment messed everything up
argc = 1
argv[0] = 0x107730040 (0x10772FEC0) (<unknown>)
argv[1] = 0x107730048 (0x0) (<null>)
Command name and arguments
argc = 1
argv[0] = <unknown>
argv[1] = <null>