int main(){
int ch = 0;
while ((ch = getchar()) != EOF)
printf("%c\n",ch);
return 0;
}
we can do it with catching spaces:
int main(){
int ch = 0;
while (isspace(ch = (char)getchar()));
printf("%c\n",ch);
return 0;
}
int ungetc(int char, FILE *stream); → pushes the character char (an unsigned char) into the specified stream so that this is available for the next read operation.
#include <stdio.h>
int main () {
FILE *fp;
int c;
char buffer [256];
fp = fopen("test", "r");
if( fp == NULL ) {
perror("Error in opening file");
return(-1);
}
while(!feof(fp)) {7h3w4lk3r/The-Hive
c = getc (fp);
/* replace ! with + */
if( c == '!' ) {
ungetc ('+', fp);
} else {
ungetc(c, fp);
}
fgets(buffer, 255, fp);
fputs(buffer, stdout);
}
return(0);
}
char functions (output)
int putc(int char, FILE *fp) → write a single character to a file or stdout
putc('\n',stdout);
takes 2 args:
1.character
2.file pointer
example redirecting the input to a file:
int main(){
int ch = 0;
while ((ch = getchar()) != EOF)
putchar(ch);
ungetc(ch, stdin); // returns EOF previously read back to stdin
printf("EOF signal detected!\n");
return 0;
}
use the above program like this:
./main < infile
int fputc(int character, FILE *stream); → writes a character (an unsigned char) to the specified stream and advances the position indicator for the stream.
example write characters a-z in a file:
int main(){
FILE *pfile = NULL;
char c = '\0';
pfile = fopen("test","w");
if (pfile != NULL){
for (c = 'A'; c <= 'Z'; c++)
fputc(c,pfile);
fclose(pfile);
}
return 0;
}
example count the number of characters and words in a file or from stdin:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]){
FILE * fp = NULL;
char ch = '\0';
int wrd = 1, character = 1;
if (argc==1)
fp = stdin;
else if (argc == 2){
if ((fp = fopen(argv[1], "r")) == NULL){
fprintf(stderr, "cant open the file %s\n",argv[1]);
exit(EXIT_FAILURE);
}
}
else {
fprintf(stderr, "usage: %s [filenme]\n",argv[0]);
exit(EXIT_FAILURE);
}
ch = getc(fp);
while (ch != EOF){
if (ch ==' ' || ch=='\n'){
wrd++;
}
else {
character++;
}
ch = getc(fp);
}
printf("\n the number of words : %d\n",wrd-1);
printf("the number of characters: %d\n",character-1);
return 0;
}
to enter EOF press Ctrl+D keys
example convert uppercase to lowercase and vice versa in a file and stdin:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
void convertCase(FILE * fptr, const char *path);
int main(){
FILE * fptr = NULL;
char path[100];
printf("enter the full path to the file: ");
scanf("%s",path);
fptr = fopen(path, "r");
if (fptr == NULL){
fprintf(stderr,"unable to open file. \n");
exit(EXIT_FAILURE);
}
convertCase(fptr,path);
return 0;
}
void convertCase(FILE * fptr, const char *path){
FILE *dest = NULL;
char ch = '\0';
dest = fopen("output","w");
if (dest == NULL){
fprintf(stderr,"unable to open file. \n");
exit(EXIT_FAILURE);
}
while ((ch = fgetc(fptr)) != EOF){
if (isupper(ch))
ch = tolower(ch);
else if (islower(ch))
ch = toupper(ch);
fputc(ch, dest);
}
fclose(fptr);
fclose(dest);
remove(path);
rename("output",path);
buffer → a pointer to a block allocated with malloc or calloc (type char **)
there is never a shortage of space cause it automatically enlarge the block of memory using realloc as needed ( getline is safe) returns the line read by getline
int fscanf(FILE _fp, const char_** format [,argument,...]);** → same as printf but on a file. returns the number of arguments that are successfully read and assigned (on success), returns EOF if the end of the file is reached before any of the conversion specifications have been processed
fscanf(myFile, "%i", &i); → reads the next integer value from the file "myFile" and stores it in the variable i
int sprintf(char _string, const char_** format,...)** → used to write formatted output to a string. we can combine several data variables into a character array, instead of printing on the console we store the output to a char buffer
sprintf(string, "%d %c %f", value, c, fit);
first parameter is a char pointer for output(buffer) the function returns the number of characters stored in the string
this function is unsafe and vulnerable to buffer overflow
#include <stdio.h>
int main() {
char string[100];
int a = 10, b=20, c= 0;
c = a + b;
sprintf(string, "sum of %d and %d is %d",a,b,c);
puts(string);
return 0;
}
sscanf(const char _str, const char_** control_string [arg1,arg2,...]);** → allows to read formatted data from a string rather than stdin or keyboard
sscanf(buffer,"%s %d", name,&age);
first arg is a pointer to string from where to read the data returns the number of items read from the string and -1 if an error is encountered
example:
#include <stdio.h>
int main() {
char *str = "jason fedin 43";
char name[10], title[10];
int age, ret;
ret = sscanf(str, "%s %s %d", name ,title, &age);
printf("name: %s\n",name);
printf("title: %s\n",title);
printf("age: %d\n",age);
return ret;
}
fflush() → used to flush/clean a file or buffer
int fflush(FILE *fp);
fflush(buffer);
for float and double values we can print a specific width of the value like this:
float floatValue = 432.476868734;
printf("float with width of 3 : %.3f",floatValue); → %.3f only print the first 3 sections
output: 432.476
for integer input always use '&' before variable name
#include <stdio.h>
int main() {
char str[100];
int i;
printf("Enter a value:");
scanf("%d", &i);
printf("\nYou entered: %d\n", i);
return 0;}
Printing system error messages
perror("error text"); → used for printing error messages followed by system stderr
returns the number of items that it successfully reads . while using scanf() to read a value for one of the basic variable types, prepend the variable name with an & sign . while using scanf() to read a string into a character array, don't use an & sign.example:
