calloc 返回指向自身的指针

Question

我在 Tiva C launchpad (ARM Cortex M4) 上分配内存时遇到问题，我想做的是在某个时候动态分配指向另一个结构内部结构的指针 calloc() 返回一个指针，该指针的值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工作方式不同。

#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*)”的指针并将其转换为(fGpio_Pin**)时，calloc()返回Spi->Pins的地址，所以基本上Spi->Pins的地址和它的值是一样的，就变成了指向自身的指针，这就是问题开始出现的时候。

堆中有足够的内存，calloc() 没有返回 NULL 指针，这可能是依赖于实现的吗？我使用的是 TI ARM 编译器和 Code Composer Studio，而不是 gcc。

也许我遗漏了什么，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(我无法发布图像，我没有足够的声誉):

在调用之后:

Answer 1

我认为您的第一个 calloc 调用分配的内存不足。从您发布的调试器的屏幕截图:

SpiRfid = (fSpi_Mod*) calloc(1, sizeof(SpiRfid));

这只会为指针分配足够的内存，而不是结构。你可能想要

SpiRfid = (fSpi_Mod*) calloc(1, sizeof(*SpiRfid));