Difference between read() and fgets() in C

Question

I want to read from a stdin stream. Is there any difference in using read() or fgets() to read from the stdin stream.

I am attaching the following two pieces of code with fgets and read. With fgets I can use a java program to write and read from the c program easily. With read and write my java program hangs waiting for the output from C program which does not come.

I am just reading a line keeping it in buf and appending A to it.

Java program is able to talk to the following program which works with fgets and puts.

#include <stdio.h>
#include <string.h>
#define SIZE  200000
main()
{
int rc;
int df;
int i;
char buf[SIZE];
for(i=0;i<=120000;i++) {
      memset(buf,'\0',SIZE);
      if(!fgets(buf,SIZE-1,stdin))
        continue;
      strcat(buf,"A_A_A_A_A_A_A");
      puts(buf);
}

}

but not with read() and write()

main()
{
int rc;
int df;
int i;
char buf[32768];
rc = fcntl(fileno(stdin), F_SETFL, O_NONBLOCK);
//rc = fcntl(fileno(stdout), F_SETFL, O_NONBLOCK);
FILE *fp;
for (;;) 
{
    int rc=-1;
    memset(buf,'\0',32768);
    //rc = fread(buf,5, 1, stdin);
    rc = read(fileno(stdin),buf,32768); 
    if (rc > 0)
    {
        strcat(buf,"B_B_B_B_B_B_B_B_B");
        write(fileno(stdout),buf,strlen(buf));

    }
}

}

Could some one tell the reason. I am still finding it hard to figure out

Answer 1

• fgets is a function, read is a system call
• fgets is standard C, read is not
• fgets is stdio buffered, read is not
• fgets works with a FILE *, read works with a file descriptor
• fgets reads until newline, read reads how much you tell it to

Need more ?

Answer 2

There is an important alternative (fread) which sits somewhat in the middle, so the question should really be broken into two parts - and both are already well answered in SO:

What is the difference between fread and read?

What is the difference between fgets and fread?

Quick rule of thumb: use fgets if you intend to read textual data line by line, use fread elsewhere.