c - 遇到 fscanf 文件指针错误问题

Question

我这里有一些代码，但我正在努力解决它，因为我似乎无法掌握这个文件指针的东西。我对使用文件还很陌生。我见过类似的其他问题，并且尝试了对其他人有效的解决方案，但由于某种原因它们对我不起作用。这是出现问题的代码部分:

    void writeRentals(char *filename, RentalT *allRentals, int totalRentals); 
int readRentals(char *filename, RentalT *allRentals);
void writeCars(char *filename, CarT *allCars, int totalCars);
int readCars(char *filename, CarT *allCars);

int main() {
    CarT allCars[255]; // a list of cars
    RentalT allRentals[255]; // a list of rentals
    int totalCars = 0; // number of all cars owned
    int totalRentals = 0; // number of rented cars
    int menu_choice, renterIndex, carId;
    char renterName[20], carMake[20];

    // read data from the files
    char rentalFilename[255];
    char carFilename[255];
    printf("Please enter the name of the rental records file:");
    fscanf("%s", &rentalFilename);
    printf("\nPlease enter the name of the car records file:");
    fscanf("%s", &carFilename);

    totalCars = readCars(carFilename, allCars);
    totalRentals = readRentals(&rentalFilename, allRentals);

这是我编译时遇到的错误:

 ----jGRASP exec: gcc -g -o carRental.exe carRental.c
carRental.c: In function 'main':
carRental.c:57:9: warning: passing argument 1 of 'fscanf' from incompatible pointer type [-Wincompatible-pointer-types]
  fscanf("%s", &rentalFilename);
         ^
In file included from carRental.c:1:0:
stdio.h:385:15: note: expected 'FILE * restrict {aka struct _iobuf * restrict}' but argument is of type 'char *'
   int __cdecl fscanf(FILE * __restrict__ _File,const char * __restrict__ _Format,...) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
               ^
carRental.c:57:15: warning: passing argument 2 of 'fscanf' from incompatible pointer type [-Wincompatible-pointer-types]
  fscanf("%s", &rentalFilename);
               ^
In file included from carRental.c:1:0:
stdio.h:385:15: note: expected 'const char * restrict' but argument is of type 'char (*)[255]'
   int __cdecl fscanf(FILE * __restrict__ _File,const char * __restrict__ _Format,...) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
               ^
carRental.c:59:9: warning: passing argument 1 of 'fscanf' from incompatible pointer type [-Wincompatible-pointer-types]
  fscanf("%s", &carFilename);
         ^
In file included from carRental.c:1:0:
stdio.h:385:15: note: expected 'FILE * restrict {aka struct _iobuf * restrict}' but argument is of type 'char *'
   int __cdecl fscanf(FILE * __restrict__ _File,const char * __restrict__ _Format,...) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
               ^
carRental.c:59:15: warning: passing argument 2 of 'fscanf' from incompatible pointer type [-Wincompatible-pointer-types]
  fscanf("%s", &carFilename);
               ^
In file included from carRental.c:1:0:
stdio.h:385:15: note: expected 'const char * restrict' but argument is of type 'char (*)[255]'
   int __cdecl fscanf(FILE * __restrict__ _File,const char * __restrict__ _Format,...) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
               ^


carRental.c:62:29: warning: passing argument 1 of 'readRentals' from incompatible pointer type [-Wincompatible-pointer-types]
  totalRentals = readRentals(&rentalFilename, allRentals);

非常感谢任何帮助，谢谢!

Answer 1

您搞乱了 scanf 和 fscanf 的使用。使用 fscanf 时您错过了要传递的第一个参数。首先打开一个文件并将相应的文件指针作为第一个参数传递给 fscanf。

使用 scanf 从控制台扫描字符串，如下所示。

printf("Please enter the name of the rental records file:");
scanf("%s", rentalFilename);
//No need of &rentalFile

然后使用文件指针打开该文件。

File *fp = fopen (rentalFilename, "r");//r for reading

然后您可以使用fscanf从文件中读取

fscanf(fp,"%s",line);//Note line is a char array
//This was just an example

您可能想查看 fscanf here 的示例.

正如 chux 在评论中所建议的，探索在 C 中扫描字符串的各种方法。 scanf 的替代方法是 gets()、fgets()。看看哪个最适合您的目的。避免使用已弃用的方法。