如何将数组从函数返回到main [英] How to return an array from function to main

问题描述

我必须使用该函数来打开文件，读取文件，将第一个值保存为以下元素(尺寸)的数量以及seq[]数组中的其他值. 我不知道如何在主目录中同时返回维度和seq[].我需要它，因为我必须在其他函数中使用这些值.如代码所示，该函数返回维(dim)，但我不知道如何返回数组.

I have to use the function to open a file, read it, save the first value as the number of following elements (dimension) and the other values in the seq[] array. I don't know how to return both dimension and seq[] in the main; I need it because I have to use these values in other functions. As the code shows, the function returns the dimension (dim), but I don't know how to return the array.

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

int leggiSequenza(char *nomeFile, int *seq) {

FILE *in;
int i;
int dim;

if((in = fopen(nomeFile, "r"))==NULL) {
    printf("Error.\n");
    return -1;
}

fscanf(in, "%d", &(dim));
printf("Find %d values.\n", dim);

if(dim < 0) {
    printf("Errore: negative value.\n");
    return -1;
}

seq = (int*) malloc(dim*sizeof(int));

i=0;
while(!feof(in) && i<(dim)) {
    fscanf(in, "%d", &seq[i]);
    i++;
}

for(i=0; i<(dim); i++) {
    printf("Value in position number %d: %d.\n", i+1, seq[i]);
}

free(seq);
fclose(in);

return dim;
}


int main(int argc, char* argv[]) {

int letturaFile;
char nomeFile[200];
int *dimensione;

printf("Insert file name:\n");
scanf("%s", nomeFile);
printf("\n");
letturaFile = leggiSequenza(nomeFile, dimensione);
dimensione = &letturaFile;
printf("dimension = %d\n", *dimensione);

return 0;
}

我认为问题的重点是*seq；我必须返回两个值(维度和数组).而且，我无法编辑该函数的参数.

I think the focus of the problem is *seq; I have to return two values (dimension and array). Moreover, I can't edit the parameters of the function.

我认为我的问题不同于这，因为在我的函数中有一个带有指针的参数，而函数没有指针...

I think my question is different from this because in my function there is a parameter with a pointer, and the function hasn't got a pointer...

推荐答案

更改函数以按指针获取数组指针:

Change the function to take the array pointer by pointer:

int leggiSequenza(char *nomeFile, int **seq);
//                                ^^^^^^^^^

然后用您的变量地址调用它:

Then call it with the address of your variable:

leggiSequenza(nomeFile, &dimensione);
//                      ^^^^^^^^^^^

在函数定义内，更改周围的细节，如下所示:

Inside the function definition, change the details around like so:

int leggiSequenza(char *nomeFile, int **seq) {
  // ...
  int *local_seq = malloc(dim*sizeof(int));

  // use local_seq in place of seq

  // free(local_seq);   // delete ...
  *seq = localsec;      // ... and replace with this

  return dim;
}

最后，调用者需要释放数组:

Finally, the caller needs to free the array:

free(dimensione);

更新:由于您已经提出了以下问题:在呼叫站点预分配内存:

Update: Since you've re-asked your question: Pre-allocate the memory at the call site:

int * p = malloc(200 * sizeof(int));

int dim = leggiSequenza(filename, p);

// ...

free(p);

这篇关于如何将数组从函数返回到main的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！