expected primary expression before ; token - c++

Question

I am trying to write a function that will split a string based on a given character and return a vector of the resulting strings but I am getting a compilation error at the line of my for loop. Any ideas why? I should be able to assign astring[0] to a char pointer correct?
/*
splits string by a given character and returns a vector of each segment
if string = "ab cd ef" and split_char = " " it will return a vector with
"ab" in first location "cd" in second location and "ef" in third location
*/
vector<string> split_string(string string_to_split, const char split_char)
{
//deletes leading split characters
int num_leading_split_char = 0;
for (char * c = string_to_split[0]; c* == split_char; c++)
{
num_leading_split_char++;
}
string_to_split.erase(0, num_leading_split_char);
//makes the split string vector
vector<string> split_string;
string temp_string = "";
for (char * c = string_to_split[0]; c*; c++)
{
if (*c == split_char)
{
split_string.push_back(temp_string); //add string to vector
temp_string = ""; //reset temp string
}
else
{
temp_string += *c; //adds char to temp string
}
}
return split_string;
}
error message:
pgm5.cpp: In function ‘std::vector >
split_string(std::__cxx11::string, char)’:
pgm5.cpp:257:34: error: invalid conversion from
‘__gnu_cxx::__alloc_traits >::value_type {aka
char}’ to ‘char*’ [-fpermissive] for (char c = string_to_split[0];
c == split_char; c++)
^
pgm5.cpp:257:40: error: expected primary-expression before ‘==’ token
for (char c = string_to_split[0]; c == split_char; c++)
^~
pgm5.cpp:269:34: error: invalid conversion from
‘__gnu_cxx::__alloc_traits >::value_type {aka
char}’ to ‘char*’ [-fpermissive] for (char c = string_to_split[0];
c; c++)
^
pgm5.cpp:269:39: error: expected primary-expression before ‘;’ token
for (char c = string_to_split[0]; c; c++)
^
Compilation failed.

Answer 1

I should be able to assign std::string str[0] to a char* pointer correct?
No. str[0] is a char literal not a char* pointer. Your complier is giving you this exact error. Since you're already using std::string why not just simply leverage some of the nice operations it provides for you like substr and find so you don't need to reinvent the wheel or maybe it's a flat tire in your case (kidding). Also, it's a good idea to pass non-POD types that you're not modifying as const references to avoid unnecessary copies i.e. const std::string &. I know in your code there is an erase operation, but in this example there is no need to modify the string being passed in.
std::vector<std::string> split_string(const std::string &string_to_split, char delim)
{
std::vector<std::string> results;
size_t match = 0;
size_t found = 0;
// match each part of string_to_split on delim and tokenize into results
// if delim char is never found then return empty vector
while ((found = string_to_split.find(delim, match)) != std::string::npos)
{
results.push_back(string_to_split.substr(match, found - match));
match = found + 1; // start again at next character
}
// after the loop, if any match was found store the last token
if (match != 0)
{
results.push_back(string_to_split.substr(match));
}
return results;
}
If you are tokenizing on spaces you can use it like this.
std::string test("This is a test.");
std::vector<std::string> tokenized = split_string(test, ' ');
for (const auto& s : tokenized)
{
std::cout << "s=" << s << std::endl;
}
Which will yield the following results.
s=This
s=is
s=a
s=test.

Answer 2

Try this you can try it at http://cpp.sh/8r6ze:
#include <sstream> // std::istringstream
#include <string>
#include <vector>
#include <iostream>
std::vector<std::string> split_string(const std::string string_to_split,
const char delimiter)
{
std::vector<std::string> tokens;
std::string token;
std::istringstream tokenStream(string_to_split);
while (std::getline(tokenStream, token, delimiter))
{
tokens.push_back(token);
}
return tokens;
}
int main ()
{
const std::string theString{"thy with this"};
for (const auto &s:split_string(theString,' ')){
std::cout << s <<std::endl;
}
return 0;
}