Difference between scanf() and fgets()

Question

I want to know what is the difference between fgets() and scanf() . I am using C as my platform.

Answer 1

There are multiple differences. Two crucial ones are:

• fgets() can read from any open file, but scanf() only reads standard input.
• fgets() reads 'a line of text' from a file; scanf() can be used for that but also handles conversions from string to built in numeric types.

Many people will use fgets() to read a line of data and then use sscanf() to dissect it.

Answer 2

int scanf(const char * restrict format, ...);

scanf(3) searches for certain pattern defined by the format argument on the given input known as stdin , where the pattern is defined by you. The given input to scanf(3) , depending on its variant (scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf), could be a string or a file.

char *fgets(char * restrict str, int size, FILE * restrict stream);

fgets(3) just reads a line from the input file stream and copy the bytes as null terminating string to the buffer str and limit the output to the buffer to given bytes in size .

Answer 3

Scanf does not perform bounds checking. fgets is likely going to be the better choice. You can then use sscanf() to evaluate it.

Good discussion of the topic here- http://cboard.cprogramming.com/c-programming/109243-scanf-vs-fgets.html

How do you allow spaces to be entered using scanf? (That was my evil twin getting lectured for forgetting this- not me)

Answer 4

scanf parses a string you read in (or created), and fgets reads a line from an open FILE*. Or do you mean fscanf?

Answer 5

It should be noted that scanf pattern specs do allow field width limits:

scanf( " %80s", mybuffer );

But, where printf() allows the width to be passed as a variable (with '*'):

printf( "My name is %*s.\n", 20, name );

scanf() does not. (It interprets the '*' as a flag to suppress/ignore the field entirely.) Which means you end up doing things like this:

#define NAMEWIDTH 40
char buffer[ NAMEWIDTH + 4 ];
...
scanf( " %40x", buffer );

and no way to connect the field width 40 in the scanf() with the buffer width 40 in the buffer declaration.

Answer 6

The main difference lies in the fact that scanf has no limits on the number of characters that can be read (in its default use), while fgets has a maximum number of char that can be read.

See the prototype of the two functions:

char * fgets (char * dest, int size, FILE * stream);

int scanf (const char * format, ...);

You can see that the second parameter of fgets imposes to read at most size char.

Another clear difference is the return value: fgets return a pointer to dest on success; scanf return the number of input items successefully matched and assigned. Then, the scanf function scans input according to format , and reads input from the standard input stream stdin , while fgets reads input from FILE * stream as default.

In conclusion, you could use scanf to read data from a FILE and insert them into a fixed-size array (for example) does not have much sense. An advantage of scanf is the formatting of output data: if the function reads 12345\\n , the output is 12345 , while the fgets reads and returns till \\n (included), adding a \\0 in the end as a string terminator.