c - C 中的 fscanf() - 需要帮助使用指针表示法读取文件

Question

花了一两个小时尝试调试这个，但无法弄清楚为什么它不能正确读取我的文件。

FILE *input;
int numAccounts = 7;
char **accountNames = malloc(sizeof(char)*numAccounts*10);
int *accountNumbers = malloc(sizeof(int)*numAccounts);
float *accountValues = malloc(sizeof(float)*numAccounts);
char *fileName = malloc(sizeof(char)*20);
input=fopen("input.txt","r");
int i;

for(i=0;i<numAccounts;i++) {
    fscanf(input,"%s%d%f",*(accountNames+i),accountNumbers+i,accountValues+i);
    printf("\n%s %d %f", *(accountNames+i), *(accountNumbers+i), *(accountValues+i));
}
fclose(input);
return 0; 

这是 input.txt

Brown 1435 234.55
Dunn 2091 2011.75
Smith 8766 945.05
Stone 4530 0.0
Becker 9073 6235.75
Rich  1003 -42.00
Doe 6739 3655.80

谢谢!

Answer 1

您应该从非动态分配开始，

int main()
{
    FILE *input = NULL;
    int numAccounts = 7;

    char accountNames[20] = "";
    int accountNumbers = 0;
    float accountValues = 0;

    input=fopen("input.txt","r");
    int i;

    for(i=0;i<numAccounts;i++) 
    {
        fscanf(input,"%s %d %f",accountNames,&accountNumbers,&accountValues);
        printf("\n%s %d %f\n", accountNames, accountNumbers, accountValues);
    }
    fclose(input);
    return 0; 
}

<小时/>

如果您必须进行动态分配，那么这个指向字符的指针分配是不正确的:char **accountNames = malloc(sizeof(char)*numAccounts*10);

您需要首先分配 char * 的 numAccounts，然后为每个 char * 分配 10 个字符。可以按如下方式完成:

    char **accountNames = malloc(sizeof(char*)*numAccounts);    // allocate numAccounts of char *
    int i;
    for( i=0; i < numAccounts; i++ )
    {
        *(accountNames + i) = malloc(sizeof(char)*10);            // allocate 10 of char
    }

所以这应该有效:

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

int main()
{
    FILE *input = NULL;
    int numAccounts = 7;

    char **accountNames = malloc(sizeof(char*)*numAccounts);    // allocate numAccounts of char *
    int i;
    for( i=0; i < numAccounts; i++ )
    {
        *(accountNames + i) = malloc(sizeof(char)*10);            // allocate 10 of char
    }
    int *accountNumbers = malloc(sizeof(int)*numAccounts);
    float *accountValues = malloc(sizeof(float)*numAccounts);

    input=fopen("input.txt","r");
    for(i=0; i<numAccounts; i++)
    {
        fscanf(input,"%s%d%f",*(accountNames+i), accountNumbers+i, accountValues+i);
        printf("\n%s %d %f", *(accountNames+i), *(accountNumbers+i), *(accountValues+i));
    }
    fclose(input);
    return 0; 
}