Possible Duplicate:
Reading string from input with space character?
I am facing problem in taking a string(technically character array) as input. Suppose i have the following declaration:
char* s;
I have to input a string using this char pointer till i hit "enter", please help! Thanx in advance.
In both C and C++ you can use the fgets function, which reads a string up to the new line. For example
char *s=malloc(sizeof(char)*MAX_LEN);
fgets(s, MAX_LEN, stdin);
will do what you want (in C). In C++, the code is similar
char *s=new char[MAX_LEN];
fgets(s, MAX_LEN, stdin);
C++ also supports the std::string class, which is a dynamic sequence of characters. More about the string library: http://www.cplusplus.com/reference/string/string/. If you decide to use strings, then you can read a whole line by writing:
std::string s;
std::getline(std::cin, s);
Where to find: the fgets procedure can be found at the header <string.h>, or <cstring> for C++. The malloc function can be found at <stdlib.h> for C, and <cstdlib> for C++. Finally, the std::string class, with the std::getline function are found at the file <string>.
Advice(for C++): if you are not sure which one to use, C-style string or std::string, from my experience I tell you that the string class is much more easy to use, it offers more utilities, and it is also much faster than the C-style strings. This is a part from C++ primer:
As is happens, on average, the string class implementation executes considerably
faster than the C-style string functions. The relative average execution times on
our more than five-year-old PC are as follows:
user 0.4 # string class
user 2.55 # C-style strings
First thing is to take input into this string you have to allocate memory. After that you can use gets or fgets or scanf
You can use cin>>variable_name; if input is without space. For input with space use gets(variable_name) in c++
the s should be allocated before starting filling on it
1) If you do not know in advance the size of inputed string you can use realloc
char* s = calloc(1,sizeof(char));
char t;
int len;
while(scanf("%c", &t)==1)
{
if(t== '\n')
break;
len = strlen(s);
s= realloc(s,len+1);
*(s+len) = t;
*(s+len+1) = '\0';
}
2) Now If you know in advance the size of your input string max length, you can read directly your string into an array of char with scanf in this way:
char s[256] // Let's assume that the max length of your input string is 256
scanf("%[^\r\n]",s) // this will read your input characters till you heat enter even if your string contains spaces
Hmmm, since the OP has stated:
I have to input a string using this char pointer till i hit "enter"
Thought I'd give this a shot, top of my head, this is a dynamic buffer, using malloc and realloc using pointers. However, it may contain bugs, but the gist is there! Nitpicky aside...
Apologies if the code does look awful... ::)
char *ptr = NULL, *temp_ptr = NULL;
int c = 0, chcount = 0, enter_pressed = 0;
do{
c = fgetc(stdin);
if (c != '\n' || c != -1){
chcount++;
if (ptr == NULL){
ptr = malloc(sizeof(char) + chcount + 1);
if (ptr != NULL) ptr[chcount] = c;
else printf("ABORT!\n");
}else{
temp_ptr = realloc(ptr, chcount + 1);
if (temp_ptr != NULL){
ptr = temp_ptr;
ptr[chcount] = c;
}else{
// OK! Out of memory issue, how is that handled?
break;
}
}
}else{
enter_pressed = 1;
}
}while (!enter_pressed);
ptr[chcount] = '\0'; // nul terminate it!
