[英]variable definition by fscanf textfile.txt in C
I have a textfile.txt containing variable definitions line by line, eg length = 1.1m我有一个 textfile.txt 包含逐行变量定义,例如长度 = 1.1m
Using fscanf
I want to store in my variable double length
the value 1.1使用fscanf
我想将值 1.1 存储在我的可变double length
中
Can someone give me some hints how to use fscanf in this case having a '=' seperator?有人可以给我一些提示,在这种情况下如何使用 fscanf 有一个 '=' 分隔符?
Thanks in advance!提前致谢!
Edit: Here is an exemplary inputfile.txt showing its structure:编辑:这是一个示例 inputfile.txt 显示其结构:
[elements]
Number of elements = 2
length_1 = 1.5m
length_2 = 2.1m
velocity_1 = 0.35m/s
velocity_2 = 0.11m/s
[cells]
Number of cells = 2
cell_1 = 0.0m
cell_2 = 1.3m
I want to extract the parameters of both sections to two different structs.我想将两个部分的参数提取到两个不同的结构中。
A simple program to read a formatted file:一个读取格式化文件的简单程序:
#include <stdio.h>
int main(void) {
FILE *fp = fopen("data.txt", "r");
float length;
if (fp == NULL) {
printf("The file was failed to open.\n");
return -1;
}
while (fscanf(fp, "%*s %*s %f", &length) == 1)
printf("%f", length);
return 0;
}
Notice that we've used请注意,我们使用了
%*s %*s %f
format %*s
string skips the word from reading it.格式%*s
字符串会跳过阅读该单词。
The file data.txt
looks something like:文件data.txt
类似于:
length = 5.324325m
Then you will get an output of:然后你会得到一个 output :
5.324325
You can now clearly see the strings are truncated and the value is successfully assigned to the variable.您现在可以清楚地看到字符串被截断并且值已成功分配给变量。
Assuming if your text file is something like this:假设您的文本文件是这样的:
length = 1.2m
length = 3.4m
length = 12.4m
Then you can read it using this code:然后您可以使用以下代码阅读它:
FILE* filePtr = fopen("textfile.txt","r");
if (filePtr==NULL)
{
printf("no such file.");
return 0;
}
float num;
while (fscanf(filePtr,"length = %f", &num)==1)
printf("%f\n", num);
fclose(filePtr);
For more information for reading from file, check this link有关从文件读取的更多信息,请查看此链接
Here a way to do, the two sections can be given in any order, or only one can be given, or even none:这里有一个办法,可以按任意顺序给出两个部分,也可以只给出一个,甚至不给出:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct Element {
double length;
double velocity;
} Element;
void * read_section(FILE * fp, const char * what, int * n, size_t sz)
{
if (*n != 0) {
fprintf(stderr, "invalid file, several sections [%s]\n", what);
exit(-1);
}
char fmt[64];
sprintf(fmt, " Number of %s = %%d", what); /* notice space at beginning */
if (fscanf(fp, fmt, n) != 1) {
fprintf(stderr, "invalid file, expected 'Number of %s = <n>'\n", what);
exit(-1);
}
if (*n <= 0) {
fprintf(stderr, "number of %s must be > 0\n", what);
exit(-1);
}
void * r = malloc(*n * sz);
if (r == NULL) {
fprintf(stderr, "not enough memory for %d %s\n", *n, what);
exit(-1);
}
return r;
}
void read_var(FILE * fp, const char * var, const char * unity, int rank, double * v)
{
char fmt[64];
sprintf(fmt, " %s_%d = %%lg%s", var, rank, unity); /* notice space at beginning */
if (fscanf(fp, fmt, v) != 1) {
fprintf(stderr, "invalid file, expected '%s_%d = <val>%s'\n", var, rank, unity);
exit(-1);
}
}
int main(int argc, char ** argv)
{
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", *argv);
exit(-1);
}
FILE * fp = fopen(argv[1], "r");
if (fp == NULL) {
perror("cannot open file");
exit(-1);
}
int nelts = 0;
Element * elts = NULL;
int ncells = 0;
double * cells = NULL;
char line[32];
int i;
while (fscanf(fp, " %31s", line) == 1) { /* notice space at beginning of format */
if (!strcmp(line, "[elements]")) {
elts = read_section(fp, "elements", &nelts, sizeof(*elts));
for (i = 0; i != nelts; ++i)
read_var(fp, "length", "m", i+1, &elts[i].length);
for (i = 0; i != nelts; ++i)
read_var(fp, "velocity", "m/s", i+1, &elts[i].velocity);
}
else if (!strcmp(line, "[cells]")) {
cells = read_section(fp, "cells", &ncells, sizeof(*cells));
for (i = 0; i != ncells; ++i)
read_var(fp, "cell", "m", i+1, &cells[i]);
}
else {
fputs("invalid file, section header expected\n", stderr);
exit(-1);
}
}
fclose(fp);
/* to check */
printf("%d elements:\n", nelts);
for (i = 0; i != nelts; ++i)
printf("%d) length=%g, velocity=%g\n", i, elts[i].length, elts[i].velocity);
printf("\n%d cells:", ncells);
for (i = 0; i != ncells; ++i)
printf(" %g", cells[i]);
putchar('\n');
free(elts);
free(cells);
return 0;
}
Notice the space at the beginning of the formats when it is needed to bypass newlines (and possible other spaces).当需要绕过换行符(以及可能的其他空格)时,请注意格式开头的空格。
Compilation and executions with your example:使用您的示例进行编译和执行:
pi@raspberrypi:/tmp $ gcc -g -Wall x.c
pi@raspberrypi:/tmp $
pi@raspberrypi:/tmp $ cat f1
[elements]
Number of elements = 2
length_1 = 1.5m
length_2 = 2.1m
velocity_1 = 0.35m/s
velocity_2 = 0.11m/s
[cells]
Number of cells = 2
cell_1 = 0.0m
cell_2 = 1.3m
pi@raspberrypi:/tmp $ ./a.out f1
2 elements:
0) length=1.5, velocity=0.35
1) length=2.1, velocity=0.11
2 cells: 0 1.3
pi@raspberrypi:/tmp $
exchanging section order交换部分顺序
pi@raspberrypi:/tmp $ cat f2
[cells]
Number of cells = 2
cell_1 = 0.0m
cell_2 = 1.3m
[elements]
Number of elements = 2
length_1 = 1.5m
length_2 = 2.1m
velocity_1 = 0.35m/s
velocity_2 = 0.11m/s
pi@raspberrypi:/tmp $ ./a.out f2
2 elements:
0) length=1.5, velocity=0.35
1) length=2.1, velocity=0.11
2 cells: 0 1.3
pi@raspberrypi:/tmp $
only elements只有元素
pi@raspberrypi:/tmp $ cat f3
[elements]
Number of elements = 2
length_1 = 1.5m
length_2 = 2.1m
velocity_1 = 0.35m/s
velocity_2 = 0.11m/s
pi@raspberrypi:/tmp $ ./a.out f3
2 elements:
0) length=1.5, velocity=0.35
1) length=2.1, velocity=0.11
0 cells:
pi@raspberrypi:/tmp $
only cells只有细胞
pi@raspberrypi:/tmp $ cat f4
[cells]
Number of cells = 2
cell_1 = 0.0m
cell_2 = 1.3m
pi@raspberrypi:/tmp $ ./a.out f4
0 elements:
2 cells: 0 1.3
pi@raspberrypi:/tmp $
empty input file空输入文件
pi@raspberrypi:/tmp $ ./a.out /dev/null
0 elements:
0 cells:
pi@raspberrypi:/tmp $
more elements and cells更多元素和单元格
pi@raspberrypi:/tmp $ cat f
[elements]
Number of elements = 3
length_1 = 1.5m
length_2 = 2.1m
length_3 = 1.1m
velocity_1 = 0.35m/s
velocity_2 = 0.11m/s
velocity_3 = 0.33m/s
[cells]
Number of cells = 5
cell_1 = 0.0m
cell_2 = 1.3m
cell_3 = 2.3m
cell_4 = 3.3m
cell_5 = 4.3m
pi@raspberrypi:/tmp $ ./a.out f
3 elements:
0) length=1.5, velocity=0.35
1) length=2.1, velocity=0.11
2) length=1.1, velocity=0.33
5 cells: 0 1.3 2.3 3.3 4.3
pi@raspberrypi:/tmp $
and the possible error cases are checked, I encourage you to never suppose all is always ok but to check it is并且检查了可能的错误情况,我鼓励您永远不要认为一切都很好,但要检查它是
To finish if you are under Linux/Unix check your program running under valgrind , for instance:如果您在 Linux/Unix 下完成,请检查您在valgrind下运行的程序,例如:
pi@raspberrypi:/tmp $ valgrind ./a.out f
==13981== Memcheck, a memory error detector
==13981== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==13981== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==13981== Command: ./a.out f
==13981==
3 elements:
0) length=1.5, velocity=0.35
1) length=2.1, velocity=0.11
2) length=1.1, velocity=0.33
5 cells: 0 1.3 2.3 3.3 4.3
==13981==
==13981== HEAP SUMMARY:
==13981== in use at exit: 0 bytes in 0 blocks
==13981== total heap usage: 5 allocs, 5 frees, 5,560 bytes allocated
==13981==
==13981== All heap blocks were freed -- no leaks are possible
==13981==
==13981== For lists of detected and suppressed errors, rerun with: -s
==13981== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
pi@raspberrypi:/tmp $
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