如何从 c 中的 .txt 文件中读取一行数字？

Question

我正在尝试编写一个代码，该代码将从 .txt 文件的第一行读取三个数字（13.1、270.66 和 81.3），并将它们与我想要的变量相关联。 这是我尝试过的：

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

int main()
{
    char filename[100];
    printf("Enter the name (including file extension) of the file you wish to use the values from: ");
    scanf("%s",filename);
    FILE *filepointer=fopen(filename,"r");
    if (filepointer==NULL){
        printf("Error: Couldn't open file: %s",filename);
    }
    double value1;
    double value2;
    double value3;
    rewind(filepointer);
    fscanf(filepointer,"%g %g %g",&value1,&value2,&value3);
    printf("Your values are: %g %g %g",value1,value2,value3);
    fclose(filepointer);
}

仅供参考，在 .txt 文件中，值是这样设置的：13.1 270.66 81.3

Answer 1

scanf() %g用于读取float 。 您应该使用%lg来读取double 。

你还应该：

• 当fopen()失败时停止执行程序的其余部分。
• 检查scanf()和fscanf()的返回值以检查它们是否成功读取了所有请求的内容。
• 指定%s的最大字符数（最多为目标大小减去一用于终止空字符）以防止缓冲区溢出。

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

int main(void)
{
    char filename[100];
    printf("Enter the name (including file extension) of the file you wish to use the values from: ");
    if (scanf("%99s",filename) != 1){ /* specify the maximum length and check the result */
        puts("Error: failed to read file name");
        return 1;
    }
    FILE *filepointer=fopen(filename,"r");
    if (filepointer==NULL){
        printf("Error: Couldn't open file: %s",filename);
        return 1; /* stop execution when fopen() fails */
    }
    double value1;
    double value2;
    double value3;
    rewind(filepointer);
    /* use correct format specifier and check the result */
    if (fscanf(filepointer,"%lg %lg %lg",&value1,&value2,&value3) == 3){
        printf("Your values are: %g %g %g",value1,value2,value3);
    } else {
        puts("Error: failed to read numbers");
        fclose(filepointer);
        return 1;
    }
    fclose(filepointer);
}