保存结构以进行后期提取

Question

我是 C 的新手。我有一个具有特定结构的 csv 文件。我创建了结构并从 csv 文件中读取数据并使用定义的结构打印它。但是，我不需要打印结构，而是需要保存它，以便访问它以供以后处理。到目前为止，我已经明白我需要使用动态内存分配，但我现在完全迷失了。任何线索都会非常有用。

输入文件如下，

2,33.1609992980957,26.59000015258789,8.003999710083008
5,15.85200023651123,13.036999702453613,31.801000595092773
8,10.907999992370605,32.000999450683594,1.8459999561309814
11,28.3700008392334,31.650999069213867,13.107999801635742
14,7.046000003814697,23.5939998626709,6.254000186920166

到目前为止我的代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct O_data
{
   unsigned int index;
   float x;
   float y;
   float z;
};

struct O_data * deserialize_data(struct O_data *data, const char *input,   const char *separators)
{
   char *p;
   struct O_data tmp;
   if(sscanf(input, "%d,%f,%f,%f", &data->index, &data->x, &data->y, &data->z) != 7)
   return NULL;
   return data;
}

int  main(int argc, char *argv[])
{
   FILE *stream;
   char *line = NULL;
   size_t len = 0;
   ssize_t nread;
   struct O_data somedata;
   if (argc != 2) {
       fprintf(stderr, "Usage: %s <file>\n", argv[0]);
       exit(EXIT_FAILURE);
   }
   stream = fopen(argv[1], "r");
   if (stream == NULL) {
       perror("fopen");
       exit(EXIT_FAILURE);
   }
   while ((nread = getline(&line, &len, stream)) != -1) {
       deserialize_data(&somedata, line, ",");
// How do I save some data to memory here to access it later like somedata[i] for ith struct later outside main. 
       printf("index: %d, x: %f, y: %f, z: %f\n", somedata.index, somedata.x, somedata.y, somedata.z);
   }
   free(line);
   fclose(stream);
   exit(EXIT_SUCCESS);
}

Answer 1

// 如何在此处将一些数据保存到内存中，以便稍后在 main 外部访问它，例如 somedata[i] 用于第 i 个结构。

您可以使用 struct O_data 的数组，使用 malloc 然后 realloc 进行分配，然后使该数组具有未知数量的条目更长，直到您读取所有文件

---

deserialize_dat中的警告

sscanf(input, "%d,%f,%f,%f", &data->index, &data->x, &data->y, &data->z)

index 是 unsigned 但是你使用%d，必须是%u，在中的printf中也是一样的主要的

tmp 和 p 未使用，如参数 separators

---

提案可以是：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct O_data
{
   unsigned int index;
   float x;
   float y;
   float z;
};

struct O_data * deserialize_data(struct O_data *data, const char *input)
{
   return (sscanf(input, "%u,%f,%f,%f", &data->index, &data->x, &data->y, &data->z) != 7) 
     ? NULL : data;
}

int  main(int argc, char *argv[])
{
   FILE *stream;
   char *line = NULL;
   size_t len = 0;
   ssize_t nread;
   struct O_data * somedata = NULL;
   size_t nelts = 0;

   if (argc != 2) {
       fprintf(stderr, "Usage: %s <file>\n", argv[0]);
       exit(EXIT_FAILURE);
   }
   stream = fopen(argv[1], "r");
   if (stream == NULL) {
       perror("fopen");
       exit(EXIT_FAILURE);
   }
   while ((nread = getline(&line, &len, stream)) != -1) {
     if ((somedata = realloc(somedata, (nelts + 1) * sizeof(struct O_data))) == NULL) {
       fprintf(stderr, "error not enough memory");
       exit(EXIT_FAILURE);
     }
     deserialize_data(&somedata[nelts++], line);
   }
   free(line);
   fclose(stream);

   /* print and free */
   for (size_t i = 0; i != nelts; ++i)
     printf("index: %u, x: %f, y: %f, z: %f\n",
            somedata[i].index, somedata[i].x, somedata[i].y, somedata[i].z);

   free(somedata);

   exit(EXIT_SUCCESS);
}

编译和执行：

pi@raspberrypi:/tmp $ gcc -pedantic -Wall -Wextra a.c
pi@raspberrypi:/tmp $ cat f
2,33.1609992980957,26.59000015258789,8.003999710083008
5,15.85200023651123,13.036999702453613,31.801000595092773
8,10.907999992370605,32.000999450683594,1.8459999561309814
11,28.3700008392334,31.650999069213867,13.107999801635742
14,7.046000003814697,23.5939998626709,6.254000186920166
pi@raspberrypi:/tmp $ ./a.out f
index: 2, x: 33.160999, y: 26.590000, z: 8.004000
index: 5, x: 15.852000, y: 13.037000, z: 31.801001
index: 8, x: 10.908000, y: 32.000999, z: 1.846000
index: 11, x: 28.370001, y: 31.650999, z: 13.108000
index: 14, x: 7.046000, y: 23.594000, z: 6.254000

valgrind下执行：

pi@raspberrypi:/tmp $ valgrind ./a.out f
==2439== Memcheck, a memory error detector
==2439== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==2439== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==2439== Command: ./a.out f
==2439== 
index: 2, x: 33.160999, y: 26.590000, z: 8.004000
index: 5, x: 15.852000, y: 13.037000, z: 31.801001
index: 8, x: 10.908000, y: 32.000999, z: 1.846000
index: 11, x: 28.370001, y: 31.650999, z: 13.108000
index: 14, x: 7.046000, y: 23.594000, z: 6.254000
==2439== 
==2439== HEAP SUMMARY:
==2439==     in use at exit: 0 bytes in 0 blocks
==2439==   total heap usage: 9 allocs, 9 frees, 5,832 bytes allocated
==2439== 
==2439== All heap blocks were freed -- no leaks are possible
==2439== 
==2439== For counts of detected and suppressed errors, rerun with: -v
==2439== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)

注意我realloc每次只在数组中添加一个条目，如果文件中有很多值，最好在中添加多个条目而不是一个条目需要时重新分配