Question

我是指针的新手，我正在尝试实现一个简单的代码，我在其中读取和写入一个数组，并且我还搜索两个给定索引之间的最小元素。由于某种原因，write（）函数打印大值（我猜它们是存储值的位置）。我运行poz_minVal函数时也会收到SIGSECV。我知道这是一个不起眼的问题，但任何帮助都会非常感激！

代码如下：

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

int read(int *v, FILE *f){
    int i,length;
    fscanf(f,"%d",&length);
    v = (int *)malloc(length*sizeof(int));
    for(i=0;i<length;++i)
        fscanf(f,"%d",v+i);
    return length;
}

void write(int *v, int length, FILE *g){
    int i;
    for(i=0;i<length;++i)
        fprintf(g,"%d ",*(v+i));
    fprintf(g,"\n\n");
}

int poz_valMin(int *v, int length,int left,int right){
    int k,mini = *v; //set mini as the 1st element in v
    for(k=left;k<right;++k)
        if(*(v+k) < mini)
            mini = *(v+k);
    return mini;
}

int main(){
    FILE *f = fopen("datein.txt","r");
    FILE *g = fopen("dateout.txt","w");
    int *v, n = read(v,f);
    write(v,n,g);
    fprintf("The minimum value between the indexes 2 and 4 is: %d.\n\n",poz_valMin(v,n,2,4));
    return 0;
}

Answer 1

无论barak manos所说的是对的，但让我指出另一种定义读取功能的方法。

int * read(FILE *f){
   int *v,length;
   fscanf(f,"%d",&length);
   v = (int *)malloc(length*sizeof(int));
   for(i=0;i<length;++i)
       fscanf(f,"%d",v+i);
   return v;
}

然后在主要你应该写v = read（f）;
这看起来很干净，简化了理解。

提示：
一旦你发现写入产生垃圾，你应该打印出数组v，你可能已经发现了错误!!

Answer 2

功能read应该int** v，并指定*v = ...。

更改函数内的输入参数不会影响函数外部的参数值。

Answer 3

//int read(int *v, FILE *f) //<-- in this case v will be treated as local variable inside read() and not the parameter passed from main.
int read(int **v, FILE *f)
{
    int i,length;
    fscanf(f,"%d",&length);
    //v = (int *)malloc(length*sizeof(int));
    int *arr = (int *)malloc(length*sizeof(int));
    for(i=0;i<length;++i)
        //fscanf(f,"%d",v+i);
        fscanf(f,"%d",arr+i);

    *v = arr;  //now you are actually assigning the allocated memory to main::v
    return length;
}

read(&v,f);  //call read like this.

Answer 4

以下代码：

将评论纳入问题，但良好的变量命名
干净地编译
执行所需的操作
执行适当的错误检查

你应养成使用main()函数（在那些具有main()函数的文件中）作为列出的第一个函数的习惯，然后对每个函数使用适当的'prototype'语句子功能

建议使用size_t来表示绝对不能为负的值。

#include <stdio.h>  // fopen(), fclose(),
#include <stdlib.h>

size_t read(       int **v, FILE *f);
void   write(      int *v, size_t length, FILE *g );
int    poz_valMin( int *v, int left, int right );


int main( void )
{
    FILE *f = fopen("datein.txt","r");
    if( !f )
    {
        perror( "fopen for read of datain.txt failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, fopen successful

    FILE *g = fopen("dateout.txt","w");
    if( !g )
    {
        perror( "fopen for write to dataout.txt failed" );
        fclose( f ); // cleanup
        exit( EXIT_FAILURE );
    }

    // implied else, fopen for output successful

    int *v;
    size_t n = read(&v,f);

    write(v,n,g);
    fprintf( stdout,
             "The minimum value between the indexes 2 and 4 is: %d.\n\n",
             poz_valMin(v, 2, 4));

    free( v );
    fclose( f );
    fclose( g );
}



size_t read(int **v, FILE *f)
{
    //int i;
    size_t length;

    if( 1 != fscanf(f,"%lu",&length) )
    {
        perror( "fscanf failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, fscanf successful

    *v = malloc(length*sizeof(int));
    if( !v )
    {
        perror( "malloc failed" );
        fclose( f );
        exit( EXIT_FAILURE );
    }

    // implied else, malloc successful

    for(size_t i=0; i<length; ++i)
    {
        if( 1 != fscanf(f,"%d",(*v)+i) )
        {
            perror( "fscanf for array values failed" );
            free( *v );
            fclose( f );
            exit( EXIT_FAILURE );
        }

        // implied else, fscanf successful
    }

    return length;
}


void write(int *v, size_t length, FILE *g)
{
    //int i;

    for( size_t i=0; i<length; ++i )
        fprintf(g,"%d ",*(v+i));

    fprintf(g,"\n\n");
}


int poz_valMin( int *v, int left, int right )
{
    int k;
    int mini = *v; //set mini as the 1st element in v

    for(k=left; k<right; ++k)
        if(*(v+k) < mini)
            mini = *(v+k);

    return mini;
}

使用C中的指针打印数组时出现问题

4 个答案: