How to read from stdin with fgets()?
Solution 1:
here a concatenation solution:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFERSIZE 10
int main() {
char *text = calloc(1,1), buffer[BUFFERSIZE];
printf("Enter a message: \n");
while( fgets(buffer, BUFFERSIZE , stdin) ) /* break with ^D or ^Z */
{
text = realloc( text, strlen(text)+1+strlen(buffer) );
if( !text ) ... /* error handling */
strcat( text, buffer ); /* note a '\n' is appended here everytime */
printf("%s\n", buffer);
}
printf("\ntext:\n%s",text);
return 0;
}
Solution 2:
You have a wrong idea of what fgets returns. Take a look at this: http://www.cplusplus.com/reference/clibrary/cstdio/fgets/
It returns null when it finds an EOF character. Try running the program above and pressing CTRL+D (or whatever combination is your EOF character), and the loop will exit succesfully.
How do you want to detect the end of the input? Newline? Dot (you said sentence xD)?
Solution 3:
Exits the loop if the line is empty(Improving code).
#include <stdio.h>
#include <string.h>
// The value BUFFERSIZE can be changed to customer's taste . Changes the
// size of the base array (string buffer )
#define BUFFERSIZE 10
int main(void)
{
char buffer[BUFFERSIZE];
char cChar;
printf("Enter a message: \n");
while(*(fgets(buffer, BUFFERSIZE, stdin)) != '\n')
{
// For concatenation
// fgets reads and adds '\n' in the string , replace '\n' by '\0' to
// remove the line break .
/* if(buffer[strlen(buffer) - 1] == '\n')
buffer[strlen(buffer) - 1] = '\0'; */
printf("%s", buffer);
// Corrects the error mentioned by Alain BECKER.
// Checks if the string buffer is full to check and prevent the
// next character read by fgets is '\n' .
if(strlen(buffer) == (BUFFERSIZE - 1) && (buffer[strlen(buffer) - 1] != '\n'))
{
// Prevents end of the line '\n' to be read in the first
// character (Loop Exit) in the next loop. Reads
// the next char in stdin buffer , if '\n' is read and removed, if
// different is returned to stdin
cChar = fgetc(stdin);
if(cChar != '\n')
ungetc(cChar, stdin);
// To print correctly if '\n' is removed.
else
printf("\n");
}
}
return 0;
}
Exit when Enter is pressed.
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <assert.h>
#define BUFFERSIZE 16
int main(void)
{
char buffer[BUFFERSIZE];
printf("Enter a message: \n");
while(true)
{
assert(fgets(buffer, BUFFERSIZE, stdin) != NULL);
// Verifies that the previous character to the last character in the
// buffer array is '\n' (The last character is '\0') if the
// character is '\n' leaves loop.
if(buffer[strlen(buffer) - 1] == '\n')
{
// fgets reads and adds '\n' in the string, replace '\n' by '\0' to
// remove the line break .
buffer[strlen(buffer) - 1] = '\0';
printf("%s", buffer);
break;
}
printf("%s", buffer);
}
return 0;
}
Concatenation and dinamic allocation(linked list) to a single string.
/* Autor : Tiago Portela
Email : [email protected]
Sobre : Compilado com TDM-GCC 5.10 64-bit e LCC-Win32 64-bit;
Obs : Apenas tentando aprender algoritimos, sozinho, por hobby. */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <assert.h>
#define BUFFERSIZE 8
typedef struct _Node {
char *lpBuffer;
struct _Node *LpProxNode;
} Node_t, *LpNode_t;
int main(void)
{
char acBuffer[BUFFERSIZE] = {0};
LpNode_t lpNode = (LpNode_t)malloc(sizeof(Node_t));
assert(lpNode!=NULL);
LpNode_t lpHeadNode = lpNode;
char* lpBuffer = (char*)calloc(1,sizeof(char));
assert(lpBuffer!=NULL);
char cChar;
printf("Enter a message: \n");
// Exit when Enter is pressed
/* while(true)
{
assert(fgets(acBuffer, BUFFERSIZE, stdin)!=NULL);
lpNode->lpBuffer = (char*)malloc((strlen(acBuffer) + 1) * sizeof(char));
assert(lpNode->lpBuffer!=NULL);
strcpy(lpNode->lpBuffer, acBuffer);
if(lpNode->lpBuffer[strlen(acBuffer) - 1] == '\n')
{
lpNode->lpBuffer[strlen(acBuffer) - 1] = '\0';
lpNode->LpProxNode = NULL;
break;
}
lpNode->LpProxNode = (LpNode_t)malloc(sizeof(Node_t));
lpNode = lpNode->LpProxNode;
assert(lpNode!=NULL);
}*/
// Exits the loop if the line is empty(Improving code).
while(true)
{
assert(fgets(acBuffer, BUFFERSIZE, stdin)!=NULL);
lpNode->lpBuffer = (char*)malloc((strlen(acBuffer) + 1) * sizeof(char));
assert(lpNode->lpBuffer!=NULL);
strcpy(lpNode->lpBuffer, acBuffer);
if(acBuffer[strlen(acBuffer) - 1] == '\n')
lpNode->lpBuffer[strlen(acBuffer) - 1] = '\0';
if(strlen(acBuffer) == (BUFFERSIZE - 1) && (acBuffer[strlen(acBuffer) - 1] != '\n'))
{
cChar = fgetc(stdin);
if(cChar != '\n')
ungetc(cChar, stdin);
}
if(acBuffer[0] == '\n')
{
lpNode->LpProxNode = NULL;
break;
}
lpNode->LpProxNode = (LpNode_t)malloc(sizeof(Node_t));
lpNode = lpNode->LpProxNode;
assert(lpNode!=NULL);
}
printf("\nPseudo String :\n");
lpNode = lpHeadNode;
while(lpNode != NULL)
{
printf("%s", lpNode->lpBuffer);
lpNode = lpNode->LpProxNode;
}
printf("\n\nMemory blocks:\n");
lpNode = lpHeadNode;
while(lpNode != NULL)
{
printf("Block \"%7s\" size = %lu\n", lpNode->lpBuffer, (long unsigned)(strlen(lpNode->lpBuffer) + 1));
lpNode = lpNode->LpProxNode;
}
printf("\nConcatenated string:\n");
lpNode = lpHeadNode;
while(lpNode != NULL)
{
lpBuffer = (char*)realloc(lpBuffer, (strlen(lpBuffer) + strlen(lpNode->lpBuffer)) + 1);
strcat(lpBuffer, lpNode->lpBuffer);
lpNode = lpNode->LpProxNode;
}
printf("%s", lpBuffer);
printf("\n\n");
// Deallocate memory
lpNode = lpHeadNode;
while(lpNode != NULL)
{
lpHeadNode = lpNode->LpProxNode;
free(lpNode->lpBuffer);
free(lpNode);
lpNode = lpHeadNode;
}
lpBuffer = (char*)realloc(lpBuffer, 0);
lpBuffer = NULL;
if((lpNode == NULL) && (lpBuffer == NULL))
{
printf("Deallocate memory = %s", (char*)lpNode);
}
printf("\n\n");
return 0;
}
Solution 4:
Assuming that you only want to read a single line, then use LINE_MAX, which is defined in <limits.h>:
#include <stdio.h>
#include <limits.h>
...
char line[LINE_MAX];
...
if (fgets(line, LINE_MAX, stdin) != NULL) {
...
}
...