Splitting a C++ std::string using tokens, e.g. ;
I find std::getline()
is often the simplest. The optional delimiter parameter means it's not just for reading "lines":
#include <sstream>
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<string> strings;
istringstream f("denmark;sweden;india;us");
string s;
while (getline(f, s, ';')) {
cout << s << endl;
strings.push_back(s);
}
}
Parse (split) a string in C++ using string delimiter (standard C++)
You can use the std::string::find()
function to find the position of your string delimiter, then use std::string::substr()
to get a token.
Example:
std::string s = "scott>=tiger";
std::string delimiter = ">=";
std::string token = s.substr(0, s.find(delimiter)); // token is "scott"
The
find(const string& str, size_t pos = 0)
function returns the position of the first occurrence ofstr
in the string, ornpos
if the string is not found.The
substr(size_t pos = 0, size_t n = npos)
function returns a substring of the object, starting at positionpos
and of lengthnpos
.
If you have multiple delimiters, after you have extracted one token, you can remove it (delimiter included) to proceed with subsequent extractions (if you want to preserve the original string, just use s = s.substr(pos + delimiter.length());
):
s.erase(0, s.find(delimiter) + delimiter.length());
This way you can easily loop to get each token.
Complete Example
std::string s = "scott>=tiger>=mushroom";
std::string delimiter = ">=";
size_t pos = 0;
std::string token;
while ((pos = s.find(delimiter)) != std::string::npos) {
token = s.substr(0, pos);
std::cout << token << std::endl;
s.erase(0, pos + delimiter.length());
}
std::cout << s << std::endl;
Output:
scott
tiger
mushroom
Split string with delimiters in C
You can use the strtok()
function to split a string (and specify the delimiter to use). Note that strtok()
will modify the string passed into it. If the original string is required elsewhere make a copy of it and pass the copy to strtok()
.
EDIT:
Example (note it does not handle consecutive delimiters, "JAN,,,FEB,MAR" for example):
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
char** str_split(char* a_str, const char a_delim)
{
char** result = 0;
size_t count = 0;
char* tmp = a_str;
char* last_comma = 0;
char delim[2];
delim[0] = a_delim;
delim[1] = 0;
/* Count how many elements will be extracted. */
while (*tmp)
{
if (a_delim == *tmp)
{
count++;
last_comma = tmp;
}
tmp++;
}
/* Add space for trailing token. */
count += last_comma < (a_str + strlen(a_str) - 1);
/* Add space for terminating null string so caller
knows where the list of returned strings ends. */
count++;
result = malloc(sizeof(char*) * count);
if (result)
{
size_t idx = 0;
char* token = strtok(a_str, delim);
while (token)
{
assert(idx < count);
*(result + idx++) = strdup(token);
token = strtok(0, delim);
}
assert(idx == count - 1);
*(result + idx) = 0;
}
return result;
}
int main()
{
char months[] = "JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC";
char** tokens;
printf("months=[%s]\n\n", months);
tokens = str_split(months, ',');
if (tokens)
{
int i;
for (i = 0; *(tokens + i); i++)
{
printf("month=[%s]\n", *(tokens + i));
free(*(tokens + i));
}
printf("\n");
free(tokens);
}
return 0;
}
Output:
$ ./main.exe
months=[JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC]
month=[JAN]
month=[FEB]
month=[MAR]
month=[APR]
month=[MAY]
month=[JUN]
month=[JUL]
month=[AUG]
month=[SEP]
month=[OCT]
month=[NOV]
month=[DEC]
How do I tokenize a string in C++?
C++ standard library algorithms are pretty universally based around iterators rather than concrete containers. Unfortunately this makes it hard to provide a Java-like split
function in the C++ standard library, even though nobody argues that this would be convenient. But what would its return type be? std::vector<std::basic_string<…>>
? Maybe, but then we’re forced to perform (potentially redundant and costly) allocations.
Instead, C++ offers a plethora of ways to split strings based on arbitrarily complex delimiters, but none of them is encapsulated as nicely as in other languages. The numerous ways fill whole blog posts.
At its simplest, you could iterate using std::string::find
until you hit std::string::npos
, and extract the contents using std::string::substr
.
A more fluid (and idiomatic, but basic) version for splitting on whitespace would use a std::istringstream
:
auto iss = std::istringstream{"The quick brown fox"};
auto str = std::string{};
while (iss >> str) {
process(str);
}
Using std::istream_iterator
s, the contents of the string stream could also be copied into a vector using its iterator range constructor.
Multiple libraries (such as Boost.Tokenizer) offer specific tokenisers.
More advanced splitting require regular expressions. C++ provides the std::regex_token_iterator
for this purpose in particular:
auto const str = "The quick brown fox"s;
auto const re = std::regex{R"(\s+)"};
auto const vec = std::vector<std::string>(
std::sregex_token_iterator{begin(str), end(str), re, -1},
std::sregex_token_iterator{}
);
How does strtok() split the string into tokens in C?
strtok()
divides the string into tokens. i.e. starting from any one of the delimiter to next one would be your one token. In your case, the starting token will be from "-" and end with next space " ". Then next token will start from " " and end with ",". Here you get "This" as output. Similarly the rest of the string gets split into tokens from space to space and finally ending the last token on "."
Expected expression before ' { ' token
Best to do the init'ing at declaration time:
double rob_size = 1.0;
double rob_tilt = 0.0;
double rob_leftcolor [3] = {1.0, 0.0, 0.0};
double rob_rightcolor [3] = {0.0, 1.0, 0.0};
Only the arrays need to be done that way, but it's best to do them all the same way.
Your alternative is
rob_leftcolor[0] = 1.0;
rob_leftcolor[1] = 0.0;
rob_leftcolor[2] = 0.0;
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