[英]C programming: Create and write 2D array of files as function
我有一个很长的程序,我想缩短它。 我经常编写2d文件数组,但是我在整个程序中重复了数十次此过程,因此我试图将其编写为一种函数,以减少我自己的错误,并使代码更短,更易于阅读。
我正在修改从函数C中分配内存2d数组获得的示例,但使用FILE数组代替。
我已经可以很容易地在main中分配2D文件数组,但是再次,我想将其作为函数来执行:
#include <stdio.h>
#include <stdlib.h>
void allocate_mem(FILE**** arr, const int n, const int m) {
arr = malloc(n*m*sizeof(FILE));
for(int i=0; i<n; i++) {
arr[i] = malloc(m*sizeof(FILE));
for (unsigned int j = 0; j < m; j++) {
char filename[64];
sprintf(filename,"tmp_%d_%d.txt",i,j);
*arr[i][j] = fopen(filename,"w");
fprintf(*arr[i][j],"blah %d %d\n",i,j);
}
}
}
void deallocate_mem(FILE**** arr, const int n, const int m){
for (int i = 0; i < n; i++) {
for (unsigned int j = 0; j < m; j++) {
fclose(*arr[i][j]);
}
free((*arr)[i]);
}
free(*arr);
}
int main() {
FILE ***array;
allocate_mem(&array,5,3);
deallocate_mem(&array,5,3);
return 0;
}
我已经尝试了几乎所有可能的方法(无论如何对我而言),但是我不断从valgrind中得到这样的错误:
==16192== HEAP SUMMARY:
==16192== in use at exit: 4,440 bytes in 3 blocks
==16192== total heap usage: 3 allocs, 0 frees, 4,440 bytes allocated
==16192==
==16192== Searching for pointers to 3 not-freed blocks
==16192== Checked 70,808 bytes
==16192==
==16192== 552 bytes in 1 blocks are still reachable in loss record 1 of 3
==16192== at 0x4C2BBA0: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16192== by 0x4EA711C: __fopen_internal (iofopen.c:69)
==16192== by 0x40080C: allocate_mem (create_file_array.c:11)
==16192== by 0x400951: main (create_file_array.c:29)
==16192==
==16192== 648 bytes in 1 blocks are still reachable in loss record 2 of 3
==16192== at 0x4C2BBA0: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16192== by 0x4007AC: allocate_mem (create_file_array.c:7)
==16192== by 0x400951: main (create_file_array.c:29)
==16192==
==16192== 3,240 bytes in 1 blocks are still reachable in loss record 3 of 3
==16192== at 0x4C2BBA0: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16192== by 0x400761: allocate_mem (create_file_array.c:5)
==16192== by 0x400951: main (create_file_array.c:29)
==16192==
==16192== LEAK SUMMARY:
==16192== definitely lost: 0 bytes in 0 blocks
==16192== indirectly lost: 0 bytes in 0 blocks
==16192== possibly lost: 0 bytes in 0 blocks
==16192== still reachable: 4,440 bytes in 3 blocks
==16192== suppressed: 0 bytes in 0 blocks
==16192==
==16192== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
==16192==
==16192== 1 errors in context 1 of 2:
==16192== Invalid write of size 8
==16192== at 0x40080D: allocate_mem (create_file_array.c:11)
==16192== by 0x400951: main (create_file_array.c:29)
==16192== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==16192==
==16192==
==16192== 1 errors in context 2 of 2:
==16192== Use of uninitialised value of size 8
==16192== at 0x40080D: allocate_mem (create_file_array.c:11)
==16192== by 0x400951: main (create_file_array.c:29)
==16192== Uninitialised value was created by a heap allocation
==16192== at 0x4C2BBA0: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16192== by 0x4007AC: allocate_mem (create_file_array.c:7)
==16192== by 0x400951: main (create_file_array.c:29)
==16192==
==16192== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
create_file_array.c
我怎样才能使allocate_mem和deallocate_mem工作?
您应该忘了听说过三颗星或四颗星。 与酒店相比,C编程使用的是逆系统:星星越多,代码的质量越差。
话虽如此,请注意,这并不是那么简单,因为您要拥有数组的类型是FILE*
。 大多数想当老手的程序员都会失败,并提出一些废话,建议使用多个for循环和多个malloc调用,以对可怜的无辜堆发起全面的攻击。
而是从main()开始。 为了节省理智,您可能希望主管道看起来像这样:
int main (void)
{
file_arr_t* array; // pointer to a 2D array
array = allocate_mem(5,3);
deallocate_mem(array);
return 0;
}
在这种情况下, allocate_mem
函数需要返回一个指向已分配数组的指针。 声明数组指针的C语法非常糟糕,因此您需要创建一个typedef来节省理智。 typedef离开指针也是一种不好的做法,因此最好typedef一个要指向的数组类型:
typedef FILE* file_arr_t[3][5]; // type is an array of 3x5 FILE*
其中file_arr_t*
是指向3x5 FILE指针数组的指针 。 ew
然后,您可以将函数编写为:
file_arr_t* allocate_mem (size_t x, size_t y)
{
file_arr_t* array = malloc(sizeof(FILE*[x][y]));
(*array)[i][j] = ... // do things with the pointer to array
return array;
}
void deallocate_mem(file_arr_t* array)
{
free(array);
}
编辑
如果您真正需要在运行时实现完全动态化的尺寸标注,恐怕您会陷入一种棘手的语法或另一种情况,因为那样便无法使用typedef。 您最终会得到这样的不可读内容:
// turning messy, avoid writing code like this.
void allocate_mem (size_t x, size_t y, FILE* (**arr_ptr)[x][y])
{
*arr_ptr = malloc(sizeof(FILE*[x][y]));
(**arr_ptr)[i][j] = something;
}
int main (void)
{
FILE* (*array)[5][3];
allocate_mem(5, 3, &array);
}
在这种情况下,我建议只使用void*
代替:
void* allocate_mem (size_t x, size_t y)
{
// omit inner-most dimension on purpose to get clearer access syntax later
FILE* (*array)[y] = malloc(sizeof(FILE*[x][y]));
// now this pointer can be used with intuitive syntax:
array[i][j] = something;
...
return array;
}
int main (void)
{
FILE* (*array)[5][3];
array = allocate_mem(5, 3);
}
第一个问题...
void allocate_mem(FILE**** arr, const int n, const int m) {
arr = malloc(n*m*sizeof(FILE)); // probably not what you want!
for(int i=0; i<n; i++) {
arr[i] = malloc(m*sizeof(FILE)); //overwrites initial value of arr when i==0!
当i == 0
您的初始指针由arr = malloc(n*m*sizeof(FILE));
被覆盖,您会泄漏(丢失可见性)该内存。 这是必须解决的。
我最初的想法是……哇! 您正在使用( FILE**** arr
)指向指针的指针。 您确实需要简化此过程。
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