How do I work with a string if I only want to print part of it?
For example, print "bcd" from "abcdef"?
I know how to work with a pointer to the beginning of a string, but I don't know how to determine the end.
void vypis(char *retezec)
{
printf("%s", retezec);
}
int main (void)
{
char *str = NULL;
size_t capacity;
getline(&str, &capacity, stdin);
vypis(str);
vypis(str+1);
}
I know how to work with a pointer to the beginning of a string, but I don't know how to determine the end.
A pointer to the last character you'd like to print is a possible solution:
void vypis(const char *retezec, const char *end)
{
while (retezec <= end && *retezec != '\0')
{
putchar(*retezec);
retezec++;
}
putchar('\n');
}
int main (void)
{
char *str = NULL;
size_t capacity = 0;
getline(&str, &capacity, stdin);
vypis(str, str + 5); //prints from str[0] to str[5]
vypis(str + 1, str + 3); //prints from str[1] to str[3]
}
Here you are.
#include <stdio.h>
int main(void)
{
char *s = "abcdef";
size_t pos = 1;
int n = 3;
printf( "%.*s\n", n, s + pos );
return 0;
}
The program output is
bcd
Or another example
#include <stdio.h>
#include <string.h>
int main(void)
{
char *s = "abcdef";
for ( int i = 0, n = ( int )strlen( s ); i < n; i++ )
{
printf( "%.*s\n", i + 1, s );
}
return 0;
}
The program output is
a
ab
abc
abcd
abcde
abcdef
You can write a generic function that can output a sub-string in any stream for example in an opened file.
#include <stdio.h>
#include <string.h>
FILE * print_substring( const char *s, size_t pos, size_t n, FILE * fp )
{
size_t len = strlen( s );
if ( pos < len )
{
if ( len - pos < n ) n = len - pos;
fprintf( fp, "%.*s", ( int )n, s + pos );
}
return fp;
}
int main(void)
{
char *s = "abcdef";
for ( int i = 0, n = ( int )strlen( s ); i < n; i++ )
{
putc( '\n', print_substring( s, 0, i + 1, stdout ) );
}
return 0;
}
The program output is
a
ab
abc
abcd
abcde
abcdef
You can try this:
#include <stdio.h>
#include <string.h>
void printSubString(const char *str, int start, int end) {
int length = strlen(str);
if (start >= length) {
return;
}
if (end >= length) {
return;
}
int index = start;
while(index <= end) {
printf("%c", str[index++]);
}
printf("\n");
}
int main() {
char *str = "Hello, world!";
printSubString(str, 3, 10);
return 0;
}
Output:
lo, worl
You can temporarily set the first character you don't want to print out (e in your example) to \0.
void vypis(char *retezec, size_t delka){
char aux = retezec[delka];
retezec[delka] = '\0';
printf("%s", retezec);
retezec[delka] = aux;
}
To make sure it also works on string literals and other const char pointers:
void vypis(const char* str, size_t delka){
char aux = retezec[delka];
char* retezec = (char*) str;
retezec[delka] = '\0';
printf("%s", retezec);
retezec[delka] = aux;
}
