如何仅将 txt 文件中的整数值读入数组？

Question

I am modifying some existing code I wrote to take in resistance and current values from a .txt file and calculate the voltage solutions. What has me stumped is that once I read a line in and use strtok to separate the integers from the other text, I don't know how to properly save those values to some variables that I can then plug into an array.

Here is an example line that is read in from the text file:

R3:56.0, R1:33.0, R2:47.0, R4:68.0, R5:75.0, IA:10.0, IB:110.0

My code below takes that line and outputs:

R3
56.0
 R1
33.0
 R2
47.0
 R4
68.0
 R5
75.0
 IA
10.0
 IB
110.0

My next goal would be to somehow identify R3 = 56.0 and R1 = 33.0 and so on, storing these values into variables named R1 , R2 , R3 , R4 , R5 , I1 , I2 so that I can use them later in my code.

#include <stdio.h>
#include <string.h>

#define LINEMAX 100

int main()
{
    FILE *dataPtr;
    char line[LINEMAX];
    char* token;
    float R1 ,R2, R3, R4, R5, I1, I2;
    double A[4][5];
    int i = 0;

    if((dataPtr = fopen("input.txt" , "r")) == NULL)
    {
        fprintf(stderr , "FILE NOT FOUND!");
    }

    while (fgets(line, LINEMAX, dataPtr) != NULL)
    {
        token = strtok (line, ",:");
        while (token != NULL)
        {
            printf("%s\n" , token);
            token = strtok (NULL, ",:");
        }
    }
    fclose(dataPtr);

Answer 1

Here are a couple of suggestions to help you along parsing each line into the values you need. Rather than 7 separate variables, R1, R2, R3, R4, R5, I1, I2 , just declare an array of double (using float just introduces more rounding error, and doesn't really buy any great savings in speed on modern processors). Store your values in order in the array (eg R1 at index 0 , R2 at index 1 , and so on). That way if you have multiple lines of the same data, it's just a matter of filling a temporary array of 7 elements and a memcpy to an array of them.

You have done a good job using a #define for LINEMAX to avoid sprinkling Magic-Numbers throughout your code. You can do the same thing for string constants as well, eg

#define MAXC 1024       /* if you need a constant, #define one (or more) */
#define TOKLEN 32       /* size for temporary token storage */
#define NELEM   7       /* number of elements to separate (R1-5, IA, IB) */
#define DELIM ",\n"     /* delimiter for strtok */

In parsing your line of data, you will need to map strings like "R1" to indexes and need a way to map indexes to strings (so you can do the reverse). A handy way when the number of mappings is small like here is just to use an enum and an array-of-pointers to string literals, eg

/* enum for mapping names to index */
enum { R1, R2, R3, R4, R5, IA, IB };
/* array for mapping index to names */
const char *id[] = { "R1", "R2", "R3", "R4", "R5", "IA", "IB" };

It is just another way to avoid sprinkling string literals throughout your code as well as providing a mapping that let's you avoid, eg

            if (strcmp (tmp, "R1") == 0)
                a[R1] = d;
            else if (strcmp (tmp, "R2") == 0)
                a[R2] = d;
            ...

And, instead use the following which leaves your single definition of id at the top as the only place you have to change the string mappings should they change in the future, eg

            if (strcmp (tmp, id[R1]) == 0)
                a[R1] = d;
            else if (strcmp (tmp, id[R2]) == 0)
                a[R2] = d;
            ...

For the parsing of values into the respective array indexes, you would simply read each line into your buffer, tokenize the line with strtok to obtain the comma-separated-values, and then use sscanf on the tokens to parse the name and value from each token, eg

int main (int argc, char **argv) {

    char buf[MAXC];     /* buffer to hold each line */
    ...
    while (fgets (buf, MAXC, fp)) { /* read each line into buf */
        char tmp[TOKLEN];           /* temporary storage for R3, etc.. */
        double d, a[NELEM] = {0.};  /* temporary double and array */
        /* tokenize line */
        for (char *p = strtok(buf, DELIM); p; p = strtok(NULL, DELIM)) {
            /* separate token into tmp string and double value in array */
            if (sscanf (p, " %31[^:]:%lf", tmp, &d) != 2) {
                fputs ("error: bad token format\n", stderr);
                goto nextline;  /* goto steps over code to process full arr */
            }
            ... /* compare tmp value here and store in-order in array */
        }
        ... /* handle whatever additional processing on array needed here */
        nextline:;      /* label for nextline */
    }

( note: the a[NELEM] = {0.}; array is initialized all zero so if for some reason a line is missing a value, you don't invoke undefined behavior attempting to access an uninitialized value)

Where above the /* compare tmp value ... */ logic would simply be:

            /* compare value in tmp store in-order in array */
            if (strcmp (tmp, id[R1]) == 0)
                a[R1] = d;
            else if (strcmp (tmp, id[R2]) == 0)
                a[R2] = d;
            else if (strcmp (tmp, id[R3]) == 0)
                a[R3] = d;
            else if (strcmp (tmp, id[R4]) == 0)
                a[R4] = d;
            else if (strcmp (tmp, id[R5]) == 0)
                a[R5] = d;
            else if (strcmp (tmp, id[IA]) == 0)
                a[IA] = d;
            else if (strcmp (tmp, id[IB]) == 0)
                a[IB] = d;
            else {
                fputs ("error: unrecognized format.\n", stderr);
                goto nextline;
            }

And for the further processing, for the example we simply output the values in order, eg

        for (int i = 0; i < NELEM; i++) /* output line results */
            printf ("got %s = %.2f\n", id[i], a[i]);

A short example that takes your line of input and fully separates the double values into an array in-order of R1-5, IA, IB would be:

#include <stdio.h>
#include <string.h>

#define MAXC 1024       /* if you need a constant, #define one (or more) */
#define TOKLEN 32       /* size for temporary token storage */
#define NELEM   7       /* number of elements to separate (R1-5, IA, IB) */
#define DELIM ",\n"     /* delimiter for strtok */

/* enum for mapping names to index */
enum { R1, R2, R3, R4, R5, IA, IB };
/* array for mapping index to names */
const char *id[] = { "R1", "R2", "R3", "R4", "R5", "IA", "IB" };

int main (int argc, char **argv) {

    char buf[MAXC];     /* buffer to hold each line */
    /* use filename provided as 1st argument (stdin by default) */
    FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;

    if (!fp) {  /* validate file open for reading */
        perror ("file open failed");
        return 1;
    }

    while (fgets (buf, MAXC, fp)) { /* read each line into buf */
        char tmp[TOKLEN];           /* temporary storage for R3, etc.. */
        double d, a[NELEM] = {0.};  /* temporary double and array */
        /* tokenize line */
        for (char *p = strtok(buf, DELIM); p; p = strtok(NULL, DELIM)) {
            /* separate token into tmp string and double value in array */
            if (sscanf (p, " %31[^:]:%lf", tmp, &d) != 2) {
                fputs ("error: bad token format\n", stderr);
                goto nextline;  /* goto steps over code to process full arr */
            }
            /* compare value in tmp store in-order in array */
            if (strcmp (tmp, id[R1]) == 0)
                a[R1] = d;
            else if (strcmp (tmp, id[R2]) == 0)
                a[R2] = d;
            else if (strcmp (tmp, id[R3]) == 0)
                a[R3] = d;
            else if (strcmp (tmp, id[R4]) == 0)
                a[R4] = d;
            else if (strcmp (tmp, id[R5]) == 0)
                a[R5] = d;
            else if (strcmp (tmp, id[IA]) == 0)
                a[IA] = d;
            else if (strcmp (tmp, id[IB]) == 0)
                a[IB] = d;
            else {
                fputs ("error: unrecognized format.\n", stderr);
                goto nextline;
            }
        }
        for (int i = 0; i < NELEM; i++) /* output line results */
            printf ("got %s = %.2f\n", id[i], a[i]);

        nextline:;      /* label for nextline */
    }

    if (fp != stdin)    /* close file if not stdin */
        fclose (fp);

    return 0;
}

Example Use/Output

Using your line of input in the file dat/rnumval.txt , you would receive:

$ ./bin/readrnumval dat/rnumval.txt
got R1 = 33.00
got R2 = 47.00
got R3 = 56.00
got R4 = 68.00
got R5 = 75.00
got IA = 10.00
got IB = 110.00

Which is just one way of conveniently mapping the separate values into identifiable indexes within the array allowing you to map names and indexes. (which is why I would recommend leaving your names and literals matching with the data in your input, eg IA, IB instead of I1, I2 -- up to you, just more work)

Look things over and let me know if you have further questions.