Why are my variables in my struct changing?

I am trying to set up an SD card on an Intel Board D2000 Quark. The problem, I am encountering is that my variables in my struct change at a certain point in the program. I figured out when the variables are changing but I do not have an idea how to fix it.

The reason I am using C instead of C++ is that the compiler of Intel Microcontrollers Studio does not let my use C++.

Below, I copied some of the relevant code.

SD* sdCard;
uint8_t readData(uint32_t block, uint16_t offset, uint16_t count, uint8_t* dst){
    if(count == 0){
        return true;
    }
    if((count + offset) > 512){
        goto fail;
    }
    if(!sdCard->inBlock_ || block != sdCard->block_ || offset < sdCard->offset_){
        sdCard->block_ = block;
        if(sdCard->type_ != SD_CARD_TYPE_SDHC){
            block <<=9;
        }
        uint8_t result = sendCommand(CMD17, block);
        if(result){
            goto fail;
        }
        if(!waitStartBlock()){
            goto fail;
        }
        sdCard->offset_ = 0;
        sdCard->inBlock_ = 1;
    }

    for(; sdCard->offset_ < offset; sdCard->offset_++){
        spiRecieve();
    }
    for(uint16_t i = 0; i < count; i++){
        dst[i] = spiRecieve();
    }
    sdCard->offset_ += count;
    if(!sdCard->partialBlockRead_ || sdCard->offset_ >= 512){
        readEnd();
    }
    QM_PUTS("RD FINISH");
    return true;

    fail:
    QM_PUTS("RD FAIL");
    return false;}

The moment the variables change is sdCard->block_ = block;. First it is a certain value. After this statement the value is 0xFFFFFFFF; This happens to every variable in the struct.

My struct looks like this:

typedef struct SDcard{
uint32_t block_ ;
uint8_t errorCode_;
uint8_t inBlock_;
uint16_t offset_;
uint8_t partialBlockRead_;
uint8_t status_;
uint8_t type_;
}SD;

Update for the comments: This is my temporary main:

SD sdCard;

int main(void)
{
if(!SDInit(&sdCard)){
    QM_PRINTF("ERROR1\n");
}
while(1){}
}

If anyone knows a solution or has some questions, please let me know.

You are improperly initializing sdCard. Currently you are assigning the value of sdCard to be a pointer to its own location on the stack. Instead, do SDInit(malloc(sizeof(SD)));.

Personally, I would not even have that initialization function. I would just do SD * sdCard = malloc(sizeof(SD));

EDIT: In response to Peter's point, you could also do this and ignore the instantiation function:

SD sdCard;