C不加载从文件信息(FREAD,FWRITE)
问题描述:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SLENG 50 //just a random value
typedef struct Song
{
char *name;
char *nameSong;
char *timeSong;
int date;
} Song;
void saveToFile(Song *x, int *songCount) //Saves info to the binary file
{
FILE *f = fopen("array.txt", "w");
if (f == NULL)
{
printf("Error\n");
}
fwrite(songCount, sizeof(int), 1, f);
fwrite(x, sizeof(struct Song), (*songCount), f);
fclose(f);
}
void readSong(Song *x, int *songCount) //Reads info fromt he file and writes it
{
FILE *fr = fopen("array.txt", "r");
if (fr == NULL)
{
printf("Error\n");
}
printf("Songs:\n");
fread(songCount, sizeof(int), 1, fr);
fread(x, sizeof(struct Song), (*songCount), fr);
for(int i=0; i < (*songCount); i++)
{
printf("%d. %s %s %s %d\n", (i+1), x[i].name, x[i].nameSong, x[i].timeSong, x[i].date);
}
fclose(fr);
}
void insertSong(Song *x, int Count) //Inserts new song into the array.
{
printf("\nInsert name of the band:\n");
x[Count].name=malloc(SLENG * sizeof(char));
scanf("%s", x[Count].name);
printf("Insert name of the song:\n");
x[Count].nameSong=malloc(SLENG * sizeof(char));
scanf("%s", x[Count].nameSong);
printf("Insert length of the song:\n");
x[Count].timeSong=malloc(SLENG * sizeof(char));
scanf("%s", x[Count].timeSong);
printf("Insert then song was created:\n");
scanf("%d", &(x[Count].date));
printf("\n");
}
main()
{
int songCount, menuOption;
Song *x=malloc(SLENG*sizeof(char)+SLENG*sizeof(char)+SLENG*sizeof(char)+sizeof(int));
printf("1. insert song\n 2. load from file\n ");
scanf("%d", &menuOption);
switch(menuOption)
{
case(1) :
printf("Insert how many songs do you want to input?\n");
scanf("%d", &songCount);
for(int i=0; i<songCount; i++)
{
insertSong(x, i);
}
saveToFile(x, &songCount);
break;
case(2) :
readSong(x, &songCount);
break;
}
}
我有一个assingment写PROGRAMM这将输入一些数据文件,并可以从文件中读取数据,该问题可能与FWRITE或fread,当我尝试从文件加载并写入数据时,似乎崩溃了。任何想法为什么它不能正常工作?我甚至可以这样做,因为它是动态结构数组。提前致谢。C不加载从文件信息(FREAD,FWRITE)
答
为了将结构保存到文件中,它必须只包含标量值,而不是指向内存对象的指针。修改您的结构,而不是使用指针数组:
typedef struct Song {
char name[SLENG];
char nameSong[SLENG];
char timeSong[SLENG];
int date;
} Song;
,并相应修改了代码,但要注意:
- 保存和读取的结构,并从文件的二进制模式
"wb"
需要打开它和"rb"
。 - 它是很容易让人误解的来命名一个二进制文件
array.txt
。 - 写入文件时,您不需要传递计数地址,但在读取时需要传递数组指针的地址,因为您还不知道要分配多少内存。
下面是修改代码:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SLENG 50 // this value is used in the file format
typedef struct Song {
char name[SLENG];
char nameSong[SLENG];
char timeSong[SLENG];
int date;
} Song;
int saveToFile(Song *x, int songCount) { //Saves info to the binary file
FILE *f = fopen("array.bin", "wb");
if (f == NULL) {
printf("Error\n");
return -1;
}
fwrite(songCount, sizeof(int), 1, f);
int written = fwrite(x, sizeof(struct Song), songCount, f);
fclose(f);
return written;
}
int readSong(Song **x, int *songCount) { //Reads info from the file and writes it
int count = 0;
FILE *fr = fopen("array.bin", "rb");
if (fr == NULL) {
printf("Error\n");
return -1;
}
printf("Songs:\n");
fread(&count, sizeof(int), 1, fr);
*x = calloc(count, sizeof(Song));
if (*x == NULL) {
printf("Cannot allocate %d bytes of memory\n", count);
fclose(fr);
return -1;
}
int found = fread(*x, sizeof(struct Song), count, fr);
for (int i = 0; i < found; i++) {
printf("%d. %s %s %s %d\n", i + 1,
(*x)[i].name, (*x)[i].nameSong, (*x)[i].timeSong, (*x)[i].date);
}
fclose(fr);
return *songCount = found;
}
void insertSong(Song *x, int Count) { //Inserts new song into the array.
printf("\nInsert name of the band:\n");
scanf("%49s", x[Count].name);
printf("Insert name of the song:\n");
scanf("%49s", x[Count].nameSong);
printf("Insert length of the song:\n");
scanf("%49s", x[Count].timeSong);
printf("Insert then song was created:\n");
scanf("%d", &(x[Count].date));
printf("\n");
}
int main(void) {
int songCount, menuOption;
Song *x = NULL;
printf("1. insert song\n 2. load from file\n ");
scanf("%d", &menuOption);
switch (menuOption) {
case 1:
printf("Insert how many songs do you want to input?\n");
if (scanf("%d", &songCount) == 1) {
x = calloc(songCount, sizeof(Song));
for (int i = 0; i < songCount; i++) {
insertSong(x, i);
}
saveToFile(x, songCount);
}
break;
case 2:
readSong(&x, &songCount);
break;
}
free(x);
x = NULL;
return 0;
}
欢迎堆栈溢出!这听起来像你可能需要学习如何使用调试器来遍历代码。使用一个好的调试器,您可以逐行执行您的程序,并查看它与您期望的偏离的位置。如果你打算做任何编程,这是一个重要的工具。进一步阅读:[如何调试小程序](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/)。 –
指针特定于单个进程。你不能保存指针。没有办法将指针加载到另一个进程中,即使它是相同的程序。要么使用数组,要么想出一种方法来[*序列化*](https://en.wikipedia.org/wiki/Serialization)每个结构中的数据。是的,指针都是你保存的。 –
至于数组的问题,你总是无条件地为每个字符串分配'SLENG'字符。这确实比编译时固定大小的数组要好。 –