以下程序尝试使用fgets逐行读取输入文件，并使用comma delimited将每个sscanf浮点值保存到结构数组中（代码的这一方面有效精细）。问题在于程序还应检测浮点值何时丢失/为空，并为其分配浮点值1.500，然后将其保存到结构数组中。
编辑：应该在Windows上使用VS2017进行编译。
*注意：：请注意，在发布此问题之前，已经研究了以下问题：
How to check if a string returned by scanf is null
How to get scanf to continue with empty scanset
输入文件的示例（第二行缺少值）：
0.123f, 0.234f, 0.345f, 0.456f, 0.567f
1.987f, , 7.376f, 2.356f, 5.122f
9.111f, 1.234f, 7.091f, 6.672f, 9.887f
所需的输出（检测到第二行中的缺失值并将其设置为1.500 ）：
0.123 0.234 0.345 0.456 0.567
1.987 1.500 7.376 2.356 5.122
9.111 1.234 7.091 6.672 9.887
到目前为止，第一次尝试将所有5个浮点数（每个后缀为'f'）扫描为字符串，然后使用strcmp和{{检查这些字符串是否为空/空或长度为零。 1}}，最后涉及尝试再次在每个这些变量上使用strlen来将每个变量读入结构数组。
第二次尝试包括通过使用sscanf来检查sscanf是否成功，但该方法也不起作用。第三次尝试，如下所示：
if (sscanf(line, "%ff", &data[i].x) == NULL) { // ...some alert and assign 1.500}摘要：
有人知道如何将该程序修改为：
#include "stdio.h"
int main() {
typedef struct {
float x, y, vx, vy, mass;
}DATA;
FILE *file = fopen("null_detector.txt", "r");
if (file == NULL)
{
printf(stderr, "ERROR: file not opened.\n");
return EXIT_FAILURE;
}
int N= 3;
DATA* data = malloc(Nbodies * sizeof * data); // Array allocation
char line[256];
int i;
int inc = 1;
for (i = 0; i < Nbodies; i += inc)
{
fgets(line, sizeof(line), file);
// **Some info:
// Scan 5 float variables per line (this part works fine)
sscanf(line, "%ff, %ff, %ff, %ff, %ff",
&data[i].x, &data[i].y, &data[i].vx, &data[i].vy, &data[i].mass); // %ff accounts for 'f' suffix
// Now check if any of above vars are empty/NULL.
// NOTE: aware that these vars CANNOT be compared to NULL,
// but has been included to try and provide clarity for end goal
if (data[i].x == NULL)
{
//.. assign 1.500 to data[i].x
}
if (data[i].y == NULL)
{
//... same as above etc
}
// ...Repeat IF statements for all 5 vars
}
//Print the contents of array of structs to check for correct output
for (i = 0; i < Nbodies; i++)
{
printf("%.3f %.3f %.3f %.3f %.3f\n", data[i].x, data[i].y, data[i].vx, data[i].vy, data[i].mass);
}
return 0;
}
读取文件时，在文件的每一行中检测到丢失的浮点值fgets替换缺少的浮点值1.500 进行比较。我已将此比较包含在代码中，只是为了使最终目标是什么更加清晰。答案 0 :(得分：1)
您可以使用strsep分隔每一行。
str = strsep(&line, ",")
使用一个函数来设置数据值：
void set_data(DATA *dt, int count, float f) {
switch(count) {
case 0: dt->x = f; break;
case 1: dt->y = f; break;
case 2: dt->vx = f; break;
case 3: dt->vy = f; break;
case 4: dt->mass = f; break;
}
}
完整代码：
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
typedef struct {
float x, y, vx, vy, mass;
}DATA;
void set_data(DATA *dt, int count, float f) {
switch(count) {
case 0: dt->x = f; break;
case 1: dt->y = f; break;
case 2: dt->vx = f; break;
case 3: dt->vy = f; break;
case 4: dt->mass = f; break;
}
}
int main() {
FILE *file = fopen("text.txt", "r");
if (file == NULL)
{
printf( "ERROR: file not opened.\n");
return EXIT_FAILURE;
}
int N= 3;
DATA* data = malloc(N * sizeof(data)); // Array allocation
char *line;
int i;
int inc = 1;
size_t n = 0;
for (i = 0; i < N; i += inc)
{
getline(&line, &n, file);
int count = 0;
char *str;
while((str = strsep(&line, ",")) != NULL) {
if (strcmp(str, " ") == 0) {
set_data(&data[i], count, 1.5);
} else {
set_data(&data[i], count, atof(str));
}
// printf("count = %d\n", count);
// printf("token: %s\n", str);
count++;
}
}
//Print the contents of array of structs to check for correct output
for (i = 0; i < N; i++)
{
printf("%.3f %.3f %.3f %.3f %.3f\n", data[i].x, data[i].y, data[i].vx, data[i].vy, data[i].mass);
}
return 0;
}
输入：
#cat text.txt
0.123f, 0.234f, 0.345f, 0.456f, 0.567f
1.987f, , 7.376f, 2.356f, 5.122f
9.111f, 1.234f, 7.091f, 6.672f, 9.887
输出：
0.123 0.234 0.345 0.456 0.567
1.987 1.500 7.376 2.356 5.122
9.111 1.234 7.091 6.672 9.887
答案 1 :(得分：1)
在缺少输入值的情况下，如果逗号之间至少存在空格，也可以仅使用sscanf来实现。
#include <stdio.h>
int main(void) {
char *str[] = {"0.123f, 0.234f, 0.345f, 0.456f, 0.567f",
"1.987f, , 7.376f, 2.356f, 5.122f",
"9.111f, 1.234f, 7.091f, 6.672f, 9.887f"};
float float_arr[3][5];
char temp[5][7];
for (unsigned i = 0; i < 3; i++) {
if (5 != sscanf(str[i], "%6[^,],%6[^,],%6[^,],%6[^,],%6[^,]",
temp[0], temp[1], temp[2], temp[3], temp[4]))
return printf("Error\n"), 1;
for (unsigned j = 0; j < 5; j++)
if (1 != sscanf(temp[j], "%ff", &float_arr[i][j]))
float_arr[i][j] = 1.500f;
}
// printing the result
for (unsigned i = 0; i < 3; i++) {
for (unsigned j = 0; j < 5; j++)
printf("%ff ", float_arr[i][j]);
printf("\n");
}
return 0;
}
输出
0.123000f 0.234000f 0.345000f 0.456000f 0.567000f
1.987000f 1.500000f 7.376000f 2.356000f 5.122000f
9.111000f 1.234000f 7.091000f 6.672000f 9.887000f