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C fgets() function

C library function - fgets()

The fgets() function is used to read characters from the current stream position up to and including the first new-line character (\n), up to the end of the stream, or until the number of characters read is equal to n-1, whichever comes first. fgets() stores the result in a string and ends it with a null character (/0). A new-line character is included in the string if it is read. The string is empty if n equals 1.

Syntax:

char *fgets(char *str, int n, FILE *stream)

Parameters:

Name Description
str This is the variable in which the string will be stored
n This is the maximum length of the string to be read
stream Identifies an address for a file descriptor, which is an area of memory associated with an input or output stream.

Return value

  • Upon successful completion, fgets() shall return s. If the stream is at end-of-file, the end-of-file indicator for the stream shall be set and fgets() shall return a null pointer.
  • If a read error occurs, the error indicator for the stream shall be set, fgets() shall return a null pointer, and shall set errno to indicate the error.

Example: Using fgets(), read data from a file

#include<stdio.h>
int main()
{
    char string[20];
    FILE *fp;
    // Write some text in test.txt
    char str[] = "C programming tutorial.";
    fp = fopen( "test.txt" , "w" );
    fwrite(str , 1 , sizeof(str) , fp );
    fclose(fp) ;
	// Here fgets() function is used to read text fine from a file.	
	  fp=fopen("test.txt","r");
    fgets(string,30,fp);
    printf("The string is: %s",string);
    fclose(fp);
    return 0;
}

The string is: C programming tutorial.

Example: Using fgets(), read from stdin

#include<stdio.h>
int main()
{
    char text[50];
    printf("Input a string: ");
    fgets(text,50,stdin);
    printf("\nThe string is: %s",text);
    return 0;
}

Input a string: C Programming

The string is: C Programming

C Programming Code Editor:

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C Programming: Tips of the Day

Returning an array using C

You can't return arrays from functions in C. You also can't (shouldn't) do this:

char *returnArray(char array []){
 char returned [10];
 //methods to pull values from array, interpret them, and then create new array
 return &(returned[0]); //is this correct?
}

returned is created with automatic storage duration and references to it will become invalid once it leaves its declaring scope, i.e., when the function returns.

You will need to dynamically allocate the memory inside of the function or fill a preallocated buffer provided by the caller.

Dynamically allocate the memory inside of the function (caller responsible for deallocating ret)

char *foo(int count) {
    char *ret = malloc(count);
    if(!ret)
        return NULL;

    for(int i = 0; i < count; ++i) 
        ret[i] = i;

    return ret;
}

Call it like so:

int main() {
    char *p = foo(10);
    if(p) {
        // do stuff with p
        free(p);
    }

    return 0;
}

Ref : https://bit.ly/3yFIeao

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