【发布时间】：2015-04-23 04:45:07
【问题描述】：
我在 Tiva C 启动板（ARM Cortex M4）上分配内存时遇到问题，我想做的是动态分配一个指向另一个结构内结构的指针的指针，在某些时候calloc() 返回一个指针与存储指针的地址相同。
我觉得这有点难以解释，所以我编写了这段代码来说明我想要做什么，并且在 here 上运行得非常好，但它在我的应用程序中的运行方式不同。
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stddef.h>
typedef struct
{
uint32_t Pin;
uint32_t Port;
} fGpio_Pin;
typedef struct
{
uint32_t Mode;
uint32_t nPins;
fGpio_Pin** Pins;
} fSpi_Mod;
fSpi_Mod* Spi;
void printSizes (void)
{
printf("Size of uint8_t: %i bytes.\n", sizeof(uint8_t));
printf("Size of uint16_t: %i bytes.\n", sizeof(uint16_t));
printf("Size of uint32_t: %i bytes.\n", sizeof(uint32_t));
printf("Size of uint64_t: %i bytes.\n", sizeof(uint64_t));
printf("Size of fSpi_Mod*: %i bytes.\n", sizeof(fSpi_Mod*));
printf("Size of fSpi_Mod: %i bytes.\n", sizeof(fSpi_Mod));
printf("Size of fGpio_Pin**: %i bytes.\n", sizeof(fGpio_Pin**));
printf("Size of fGpio_Pin*: %i bytes.\n", sizeof(fGpio_Pin*));
printf("Size of fGpio_Pin: %i bytes.\n", sizeof(fGpio_Pin));
printf("----\n");
}
void printStructure (fSpi_Mod* Spi_Mod)
{
uint8_t i;
printf("The address of the structure is 0x%X.\n", Spi_Mod);
printf("The value of mode is 0x%X and address 0x%X.\n", Spi_Mod->Mode, &(Spi_Mod->Mode));
printf("The value of nPins is 0x%X and address 0x%X.\n", Spi_Mod->nPins, &(Spi_Mod->nPins));
printf("The value of Pins is 0x%X and address 0x%X.\n", Spi_Mod->Pins, &(Spi_Mod->Pins));
for (i = 0; i < Spi_Mod->nPins; i++)
{
printf("#%i | The pointer that points to Gpio structure is 0x%X at address 0x%X.\n", i, *(Spi_Mod->Pins + i), &(*(Spi_Mod->Pins + i)));
printf("#%i | The value of Pin of Gpio structure is 0x%X and address 0x%X.\n", i, ((*(Spi_Mod->Pins + i)))->Pin, &(((*(Spi_Mod->Pins + i)))->Pin));
printf("#%i | The value of Port of Gpio structure is 0x%X and address 0x%X.\n", i, ((*(Spi_Mod->Pins + i)))->Port, &(((*(Spi_Mod->Pins + i)))->Port));
}
printf("----\n");
}
int main()
{
uint8_t i = 0;
printf(">>>> Begin program.\n");
printSizes();
Spi = (fSpi_Mod*) calloc(1, sizeof(fSpi_Mod));
if (Spi == NULL) {
printf("Insufficient memory.\n");
return 1;
}
//printStructure(Spi);
Spi->Mode = 0x05;
Spi->nPins = 0x04;
Spi->Pins = (fGpio_Pin**) calloc(Spi->nPins, sizeof(fGpio_Pin*));
if (Spi->Pins == NULL)
{
printf("Insufficient memory.\n");
return 1;
}
//printStructure(Spi);
for (i = 0; i < Spi->nPins; i++)
{
(*(Spi->Pins + i)) = (fGpio_Pin*) calloc(1, sizeof(fGpio_Pin));
if ((*(Spi->Pins + i)) == NULL)
{
printf("Insufficient memory.\n");
return 1;
}
}
printStructure(Spi);
printf(">>>> End program.\n");
}
在我的应用程序中，当我尝试分配四个类型为“指向(fGpio_Pin*)”的指针并将其强制转换为(fGpio_Pin**) 时，calloc() 返回Spi->Pins 的地址，所以基本上是Spi->Pins 的地址和它的值是一样的，变成一个指向自己的指针，这时候问题就开始出现了。
堆中有足够的内存并且calloc() 没有返回NULL 指针，这可能与实现有关吗？我使用的是 TI ARM Compiler 和 Code Composer Studio，而不是 gcc。
也许我错过了一些东西，所以我会继续寻找。感谢您的宝贵时间。
编辑1：
这是上面代码的输出，可以正常工作。
>>>> Begin program.
Size of uint8_t: 1 bytes.
Size of uint16_t: 2 bytes.
Size of uint32_t: 4 bytes.
Size of uint64_t: 8 bytes.
Size of fSpi_Mod*: 8 bytes.
Size of fSpi_Mod: 24 bytes.
Size of fGpio_Pin**: 8 bytes.
Size of fGpio_Pin*: 8 bytes.
Size of fGpio_Pin: 8 bytes.
----
The address of the structure is 0x1DF7010.
The value of mode is 0x5 and address 0x1DF7010.
The value of nPins is 0x4 and address 0x1DF7014.
The value of Pins is 0x1DF7030 and address 0x1DF7018.
#0 | The pointer that points to Gpio structure is 0x1DF7060 at address 0x1DF7030.
#0 | The value of Pin of Gpio structure is 0x0 and address 0x1DF7060.
#0 | The value of Port of Gpio structure is 0x0 and address 0x1DF7064.
#1 | The pointer that points to Gpio structure is 0x1DF7080 at address 0x1DF7038.
#1 | The value of Pin of Gpio structure is 0x0 and address 0x1DF7080.
#1 | The value of Port of Gpio structure is 0x0 and address 0x1DF7084.
#2 | The pointer that points to Gpio structure is 0x1DF70A0 at address 0x1DF7040.
#2 | The value of Pin of Gpio structure is 0x0 and address 0x1DF70A0.
#2 | The value of Port of Gpio structure is 0x0 and address 0x1DF70A4.
#3 | The pointer that points to Gpio structure is 0x1DF70C0 at address 0x1DF7048.
#3 | The value of Pin of Gpio structure is 0x0 and address 0x1DF70C0.
#3 | The value of Port of Gpio structure is 0x0 and address 0x1DF70C4.
----
>>>> End program.
在我的应用程序中（我无法发布我没有足够声誉的图片）：
调用之后：
【问题讨论】：
-
*(Spi->Pins + i)->Spi->Pins[i]会减少混乱。还有，Do not cast the result ofmalloc()。另外，如果calloc()没有返回NULL，没有问题，保证AFAIK返回有效地址，实际问题是什么？ -
你能显示运行该程序时得到的输出吗？
-
是的，请输出，因为您在打印值指针时显然使用了运算符的
&地址错误，并且您打印了指针的地址。 -
涉及
calloc()的代码看起来不错，而且C中不需要强制转换，也不建议这样做。 -
我添加了更多信息，感谢您的帮助。
标签： c pointers memory heap-memory calloc