创建一个输入函数

Question

如何创建一个输入函数来打开输入文件并从文件读入数据？并且该文件是否必须存储在某个位置？我可以这样做，只需将它保存在我的桌面上作为文本文件？这是我到目前为止的内容

#include <stdio.h> /* NULL is defined here */ 
#include <stdlib.h> /* for malloc() */ 
#include <string.h> /* for string related functions */ 

#define NAME_LEN 10 

struct data { 
    char name[NAME_LEN]; 
    int age; 
    int weight; 
}; 

typedef struct data DATA; 

struct linked_list { 
    DATA    d; 
    struct linked_list * next; 
}; 

typedef struct linked_list ELEMENT; 
typedef ELEMENT *   LINK; 

/* function prototypes */ 
LINK create_list_from_file(const char *); 
void print_list_to_file(LINK, const char *, const char *); 
int count(LINK, const int, const int); 
LINK lookup(const DATA, LINK); 
void insert(LINK, LINK, LINK); 

nt main(int argc, char *argv[]) 
{ 
    LINK head, found, to_add; 
    char *in_file_name = "infile"; /* default input file name */ 
    char *out_file_name = "outfile"; /* default output file name */ 
    int a = 20, w = 150; /* will be used as the age limit and weight limit */ 


    /* The input and output files can be given as command line arguments */ 
    switch (argc) { 
    case 1: 
     printf("The default input and output files are %s and %s.\n", 
       in_file_name, out_file_name); 
     break; 
    case 2: 
     printf("The input file is %s and the default output file is %s.\n", 
       argv[1], out_file_name); 
     in_file_name = argv[1]; 
     break; 
    case 3: 
     printf("The input file is %s and the output file is %s.\n", 
       argv[1], argv[2]); 
     in_file_name = argv[1]; 
     out_file_name = argv[2]; 
     break; 
    default: 
     printf("The input file is %s and the output file is %s.\n", 
       argv[1], argv[2]); 
     in_file_name = argv[1]; 
     out_file_name = argv[2]; 
     printf("The remaining arguments are not used.\n"); 
    } 

/* 
1. invoke create_list_from_file() function to create a linear linked list 
    from the data in the input file, 
*/ 
    head = create_list_from_file(in_file_name); 
/* 
2. invoke print_list_to_file() function with the writing mode ("w"), 
*/ 
    print_list_to_file(head, out_file_name, "w"); 
/* 
3. invoke the count() function, 
4. output the counted result to the screen, 
*/ 
    printf("The number of people with age over %d and weight over %d is %d.\n", 
      a, w, count(head, a, w)); 
/* 
5. invoke the lookup() function and insert() function, and 
*/ 
    /* prepare an element to be looked-up and added */ 
    to_add = malloc(sizeof(ELEMENT)); 
    strcpy(to_add -> d.name, "Janet"); 
    to_add -> d.age = 21; 
    to_add -> d.weight = 150; 
    to_add -> next = NULL; 

    found = lookup(to_add -> d, head); 
    insert(head, found, to_add); 
/* 
6. invoke print_list_to_file() function with the append mode ("a"). 
*/ 
    print_list_to_file(head, out_file_name, "a"); 

/* 
repeat step 5 with an element that does not exist in the current list 
*/ 
    /* prepare an element to be looked-up and added */ 
    to_add = malloc(sizeof(ELEMENT)); 
    strcpy(to_add -> d.name, "Jerry"); 
    to_add -> d.age = 24; 
    to_add -> d.weight = 220; 
    to_add -> next = NULL; 

    found = lookup(to_add -> d, head); 
    insert(head, found, to_add); 
/* 
repeat step 6: invoke print_list_to_file() function with the append mode ("a"). 
*/ 
    print_list_to_file(head, out_file_name, "a"); 

    return 0; 
} 

Answer 1

您可以使用标准库打开计算机上几乎任何文件，包括可访问的网络存储。可以读取文本或二进制文件，包括简单的“.txt”文件。例如，您可以从文件中读取一个整数：

#include <stdio.h> 
... 
int i; 
FILE *f; 
f= fopen("D:\Temp\SomeFile.txt", "r"); 
fscanf(f, "%d", &i); 
fclose(f); 

您可以使用面向行的语义，如果你想（如上面的例子） - look C library reference for fopen等等应该有一些例子，它们很有用也。