[英]read data from txt file into a struct in C
您好我正在嘗試將逗號分隔的文件讀入 c 中的結構。 問題是它們在同一句話之間有空格,所以 fscanf 不能正常工作。
文本文件:
9780136019701,An Introduction to Organic Chemistry,Timberlake Karen,10,3.54,12-2008
9781506304212,Mathematics for Social Scientists,Kropko Jonathan,7,4.73,12-2015
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct Date
{
int year;
int month;
} Date;
typedef struct Book
{
long long int isbn;
char title[100];
char author[100];
int quantity;
int price;
Date date;
} Book;
int main() {
Book* Books;
int n_books=0;
FILE *ptr = fopen("Books.txt", "r");
if(ptr!=NULL) {
Books = (Book*)malloc(sizeof(Book));
while(!feof(ptr)) {
fscanf(ptr,"%lld",&((*(Books+n_books)).isbn));
fscanf(ptr,"%s",(*(Books+n_books)).title);
fscanf(ptr,"%s",(*(Books+n_books)).author);
fscanf(ptr,"%d",&((*(Books+n_books)).quantity));
fscanf(ptr,"%f",&((*(Books+n_books)).price));
Date date;
fscanf(ptr,"%d",&date.month);
fscanf(ptr,"%d",&date.year);
(*(Books+n_books)).date = date;
printf("Name:%s\n",Books[n_books].title);
printf("ID:%lld\n",Books[n_books].isbn);
printf("price:%f\n",Books[n_books].price);
printf("date:%d-%d\n",Books[n_books].date.month,Books[n_books].date.year);
printf("quantity:%d\n",Books[n_books].quantity);
printf("author:%s\n",Books[n_books].author);
n_books++;
Books=realloc(Books,sizeof(Book)*n_books);
}
fclose(ptr);
}
else {
printf("Couldnt load books data");
exit(0);
}
free(Books);
return 0;
}
您的程序存在以下問題:
%s
轉換格式說明符將只讀取一個單詞。while(!feof(ptr))
,這通常是錯誤的(在這種情況下也是錯誤的)。,
。%f
,您告訴fscanf
將float
存儲到int price
中。Books=realloc(Books,sizeof(Book)*n_books);
只會為您當前使用的內容分配足夠的內存,但您需要為當前使用的內容和下一本書分配足夠的內存。這是解決這些問題的解決方案:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct Date
{
int year;
int month;
} Date;
typedef struct Book
{
long long int isbn;
char title[100];
char author[100];
int quantity;
double price;
Date date;
} Book;
int main( void )
{
Book *Books;
int n_books = 0;
FILE *fp = fopen( "Books.txt", "r" );
if ( fp == NULL )
{
perror( "fopen" );
exit( EXIT_FAILURE );
}
Books = malloc( sizeof(Book) );
if ( Books == NULL )
{
fprintf( stderr, "Memory allocation error!\n" );
exit( EXIT_FAILURE );
}
while (
fscanf(
fp,
"%lld,%99[^,],%99[^,],%d,%lf,%d-%d",
&Books[n_books].isbn,
Books[n_books].title,
Books[n_books].author,
&Books[n_books].quantity,
&Books[n_books].price,
&Books[n_books].date.month,
&Books[n_books].date.year
)
== 7
)
{
printf( "Name: %s\n", Books[n_books].title );
printf( "ID: %lld\n", Books[n_books].isbn );
printf( "price: %lf\n", Books[n_books].price );
printf( "date: %d-%d\n", Books[n_books].date.month, Books[n_books].date.year);
printf( "quantity: %d\n", Books[n_books].quantity);
printf( "author: %s\n", Books[n_books].author);
n_books++;
Books = realloc( Books, sizeof(Book) * (n_books+1) );
if ( Books == NULL )
{
fprintf( stderr, "Memory allocation error!\n" );
exit( EXIT_FAILURE );
}
}
free(Books);
fclose( fp );
return 0;
}
對於問題中指定的輸入,該程序具有以下輸出:
Name: An Introduction to Organic Chemistry
ID: 9780136019701
price: 3.540000
date: 12-2008
quantity: 10
author: Timberlake Karen
Name: Mathematics for Social Scientists
ID: 9781506304212
price: 4.730000
date: 12-2015
quantity: 7
author: Kropko Jonathan
然而,同樣值得注意的是,每次循環迭代調用一次realloc
是相當低效的,因為realloc
可能每次都必須將舊內存緩沖區的全部內容復制到新內存位置。 但是,如果您有成百上千本書,這可能只會成為一個問題。 有關使用realloc
的更有效算法,請參閱我對另一個問題的回答。
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