read multidigit int from file c

问题

So I have a text file called num.txt that has a string of integers separated by a space.

So let's say num.txt contains: 5 3 21 64 2 5 86 52 3

I want to open the file in read format and get the numbers. So I can say

int iochar;
FILE *fp;

fp = fopen("num.txt", "r");
while ((iochar=getc(fp)) !=EOF){
    if(iochar!=' '){
        printf("iochar= %d\n", iochar); //this prints out the ascii of the character``
    }

^this works for single-digit numbers. but how should I handle numbers with two or three or more digits?

回答1:

Use strtol() for parsing a list of integers:

char buf[BUFSIZ];

while (fgets(buf, sizeof buf, stdin)) {
    char *p = buf;

    while (1) {
        char *end;

        errno = 0;
        int number = strtol(p, &end, 10);

        if (end == p || errno) {
            break;
        }

        p = end;

        printf("The number is: %d\n", number);
    }
}

If you wish to parse floating-point numbers, use strtod().

回答2:

Use a buffer to store read bytes until you hit the separator, then parse the string using atoi:

char simpleBuffer[12];    //max 10 int digits + 1 negative sign + 1 null char string....if you read more, then you probably don't    have an int there....
int  digitCount = 0;
int iochar;

int readNumber; //the number read from the file on each iteration
do {

    iochar=getc(fp);

    if(iochar!=' ' && iochar != EOF) {
        if(digitCount >= 11)
            return 0;   //handle this exception in some way

        simpleBuffer[digitCount++] = (char) iochar;
    }
    else if(digitCount > 0)
        simpleBuffer[digitCount] = 0; //append null char to end string format

        readNumber = atoi(simpleBuffer);    //convert from string to int
       //do whatever you want with the readNumber here...

       digitCount = 0;  //reset buffer to read new number
    }

} while(iochar != EOF);

回答3:

Why do not you read the data into buffer and use sscanf to read the integers.

char nums[900];
if (fgets(nums, sizeof nums, fp)) {
    // Parse the nums into integer. Get the first integer.
    int n1, n2;
    sscanf(nums, "%d%d", &n1, &n2);
    // Now read multiple integers
}

回答4:

char ch;
FILE *fp;
fp = fopen("num.txt","r"); // read mode

if( fp != NULL ){
    while( ( ch = fgetc(fp) ) != EOF ){
        if(ch != ' ')
           printf("%c",ch);
    }
     fclose(fp);
}

回答5:

In keeping with OPs style:
Detect groups of digits and accumulate the integer as you go.

As OP did not specify the type of integer and all examples were positive, assume type unsigned.

#include <ctype.h>

void foo(void) {
  int iochar;
  FILE *fp;

  fp = fopen("num.txt", "r");
  iochar = getc(fp);
  while (1) {
    while (iochar == ' ')
      iochar = getc(fp);
    if (iochar == EOF)
      break;
    if (!isdigit(iochar))
      break;  // something other than digit or space
    unsigned sum = 0;
    do {

      /* Could add overflow protection here */

      sum *= 10;
      sum += iochar - '0';
      iochar = getc(fp);
    } while (isdigit(iochar));
    printf("iochar = %u\n", sum);
  }
  fclose(fp);
}

来源：https://stackoverflow.com/questions/24156314/read-multidigit-int-from-file-c

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getchar

getc