In case this helps other newbies, I moved the getstring function to a separate file containing custom functions. Also, I changed getstring's logic to go ahead and double the allocated memory each time more space is required, so that all the input can be parsed more quickly. When the entire string has been read, a final call to malloc shrinks the allocated memory so that it is just enough to hold the string--e.g., 13 bytes for "I love linux" (there's always one more byte needed than the number of characters because of the '\0' string terminator).
Code:
// filename: mylib.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "mylib.h"
#define SIZE 256
char *getstring(void) // this function reads a string from command line,
{ // chops off the final \n, then shrinks allocated memory to exact bytes needed to hold the string
int mem = SIZE;
char *str = malloc(mem); // I'll keep str pointing to beginning of string...
if (str == NULL)
report_alloc_error();
char *next_char = str; // ...and next_char pointing to where next character should go
fgets(next_char, mem, stdin);
while(str[strlen(str)-1] != '\n') // when we get whole string, last char will be '\n'
{
mem *= 2;
str = realloc(str, mem);
if (str == NULL)
report_alloc_error();
next_char = str + strlen(str);
fgets(next_char, mem/2 + 1, stdin);
}
// chop off trailing newline from string
*(str + strlen(str) - 1) = '\0';
// trim mem down to exact bytes needed to hold string
mem = strlen(str) + 1;
str = realloc(str, mem);
// for debugging:
//printf("final str is %s\n", str);
//printf("final mem is %d\n", mem);
return str;
}
void clean_stdin(void)
{
int c;
do
{
c = getchar();
} while (c != '\n' && c != EOF);
}
void report_alloc_error(void)
{
printf("Memory allocation failed. Exiting.");
exit(1);
}
Code:
// filename: mylib.h
#ifndef MYLIB_H_ // This guards against including this header more than once
#define MYLIB_H_
char *getstring(void);
void clean_stdin(void);
void report_alloc_error(void);
#endif
Code:
// filename: example.c
// to compile: gcc -o example example.c mylib.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "mylib.h"
int main(void)
{
char c;
int i;
float f;
char *s;
printf("Enter a character: ");
scanf(" %c", &c); // the space tells scanf to ignore leading white space (if that's what you want).
clean_stdin(); // note that for format specifiers other than %c, scanf automatically ignores leading whitespace.
printf("Enter an integer: ");
scanf("%d", &i);
clean_stdin();
printf("Enter a float: ");
scanf("%f", &f);
clean_stdin();
printf("Enter a string: ");
s = getstring();
printf("\nYour character: %c\n", c);
printf("Your integer: %d\n", i);
printf("Your float: %f\n", f);
printf("Your string: %s\n", s);
free(s);
return 0;
}
Code:
$ gcc -o example example.c mylib.c
$ ./example
Enter a character: y some garbage 38.9
Enter an integer: 3 more garbage 89
Enter a float: 3.14159 7389junk
Enter a string: I love C programming, yes I do!
Your character: y
Your integer: 3
Your float: 3.141590
Your string: I love C programming, yes I do!
Last edited by DevuanFan; 11-12-2019 at 04:58 PM..
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