[英]Fread and pointer to structures in functions
I am working at program reading bitmap. 我正在程序中读取位图。 The thing is I wrote everything in main and need to spread out code to functions.
问题是我主要编写了所有内容,并且需要将代码分散到函数中。 I am reading information using fread using standard structure adressing but I somehow cannot acces information after leaving function.
我正在使用标准结构地址使用fread读取信息,但退出功能后无法以某种方式访问信息。 So I tried adressing structure via pointers, but fread doesn't let me to do so.
所以我通过指针尝试了地址结构,但是fread不允许我这样做。 I've read that fread isn't designed to do it via pointers.
我读过fread并非旨在通过指针来实现。 But i cannot confirm it.
但我无法确认。 And that's my question.
这就是我的问题。 How do I do it via pointers?
我该如何通过指针? And why my first try doesn't work outside function?
为什么我的第一次尝试在功能之外无法正常工作?
void odczyt_pliku_bmp(struct FileHeader fheader, struct MapHeader mheader, char *nazwa) {
FILE *fp1;
fp1 =fopen(nazwa,"rb");
if(fp1)
{
fread(&fheader.sygnatura,2,1,fp1);
//...
printf("%d\n",fheader.sygnatura);//Checking. Everything seems right there
}
else
{
printf("Error");
}
fclose(fp1);
}
And main: 主要:
int main() {
struct FileHeader fheader;
struct MapHeader mheader;
char nazwapliku, *wczyt_nazwa =&nazwapliku;
printf("Podaj nazwe pliku bitmapy: ");
scanf("%s",wczyt_nazwa);
odczyt_pliku_bmp(fheader, mheader, wczyt_nazwa);
printf("%d\n",fheader.sygnatura);// And there is random trash
return 0;
}
Another try using pointers: 另一种尝试使用指针:
void odczyt_pliku_bmp(struct FileHeader *fheader, struct MapHeader *mheader, char *nazwa) {
FILE *fp1;
fp1 =fopen(nazwa,"rb");
if(fp1)
{
fread(fheader->sygnatura,2,1,fp1);
//...
printf("%d\n",fheader->sygnatura);
}
else
{
printf("Error");
}
fclose(fp1);
}
Again main for second method: 再次主要用于第二种方法:
int main() {
struct FileHeader fheader;
struct MapHeader mheader;
char nazwapliku, *wczyt_nazwa =&nazwapliku;
printf("Podaj nazwe pliku bitmapy: ");
scanf("%s",wczyt_nazwa);
odczyt_pliku_bmp(&fheader, &mheader, wczyt_nazwa);
printf("%d\n",fheader.sygnatura);
return 0;
}
fread
needs the address of a buffer. fread
需要缓冲区的地址。 So in your second attempt, pass the address of fheader->sygnatura
: 因此,在第二次尝试中,传递
fheader->sygnatura
的地址:
fread(&fheader->sygnatura,2,1,fp1);
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