我正在尝试将结构写入文件,然后将结构读取到动态分配的内存。
如果该算法甚至可行,我不确定fread函数是否可以读取以这种方式编写的文件中的所有结构并将其存储到* ptr,以便可以从内存中访问它?
有更好的方法吗?
typedef struct num {
int num1;
int num2;
}NR;
void write() {
int successfullywritten;
FILE *f;
struct num nr;
f = fopen("dat.txt", "a");
printf("Enter first number\n");
scanf("%d", &nr.num1);
printf("Enter second number\n");
scanf("%d", &nr.num2);
successfullywritten=fwrite(&nr, sizeof num, 1, f);
printf("Succesfully written: %d\n", successfullywritten);
fclose(f);
}
void read() {
int size, entrys,i,successfullyread;
FILE *f;
f = fopen("dat.txt", "r");
struct num *ptr;
fseek(f, 0L, SEEK_END);
size = ftell(f);
printf("\nSize of file dat.txt: %d\n", size);
entrys = size / sizeof(num);
ptr = (num*)malloc(entrys * sizeof(num));
successfullyread=fread(ptr, sizeof(num), entrys, f);
printf("sucessfully Read: %d\n", successfullyread);
for (i = 0;i < entrys; i++) {
/*fread((ptr+i), sizeof(ptr), 1, f);*/
printf("%d ", (*(ptr)).num1);
printf("%d\n", (*(ptr)).num2);
}
printf("\n");printf("\n");
fclose(f);
}
int main() {
int n;
while(1){
printf("Chooose action:\n1) write to file\n2) read from file:\n");
scanf("%d", &n);
switch (n) {
case 1:
write();
break;
case 2:
read();
break;
}
}
return 0;
}
最佳答案
首先,有很多简单的错字错误,例如
类型定义名称或结构名称之间存在混淆。这个entrys = size / sizeof(num);
应该是entrys = size / sizeof(struct num);
该ptr = (num*)malloc(entrys * sizeof(num));
应该是ptr = malloc(entrys * sizeof(struct num));
。避免强制转换malloc()
的结果。
其次,找到size
后,您忘记将f
移到文件开头。例如
fseek(f, 0L, SEEK_END);
size = ftell(f);
fseek(f, 0L, SEEK_SET); /* you forgot to add this */
第三,使用
fwrite()
而不是ab
模式将数据存储到文件中&在使用
a
进行阅读时,请使用fread()
而不是rb
。同样,从文件读取后,您需要释放
r
以避免内存泄漏。free(ptr);
这是示例代码
typedef struct num {
int num1;
int num2;
}NR;
void my_write(void) {
int successfullywritten;
FILE *f;
struct num nr;
f = fopen("dat.txt", "ab");
printf("Enter first number\n");
scanf("%d", &nr.num1);
printf("Enter second number\n");
scanf("%d", &nr.num2);
successfullywritten=fwrite(&nr, sizeof(nr), 1, f);
printf("Succesfully written: %d\n", successfullywritten);
fclose(f);
}
void my_read(void) {
int size, entrys,i,successfullyread;
FILE *f;
f = fopen("dat.txt", "rb");
struct num *ptr;
fseek(f, 0L, SEEK_END);
size = ftell(f);
fseek(f, 0L, SEEK_SET);
printf("\nSize of file dat.txt: %d\n", size);
entrys = size / sizeof(struct num);
ptr = malloc(entrys * sizeof(struct num));
successfullyread=fread(ptr, sizeof(struct num), 2, f);
printf("sucessfully Read: %d\n", successfullyread);
for (i = 0;i < entrys; i++) {
/*fread((ptr+i), sizeof(ptr), 1, f);*/
printf("%d ", ptr[i].num1);
printf("%d\n", ptr[i].num2);
}
free(ptr);
printf("\n");printf("\n");
fclose(f);
}
int main(void) {
int n;
while(1){
printf("Chooose action:\n1) write to file\n2) read from file:\n");
scanf("%d", &n);
switch (n) {
case 1:
my_write();
break;
case 2:
my_read();
break;
}
}
return 0;
}
关于c - 将结构写入文件,并将结构读取到动态分配的内存,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/50680068/