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Critiques (even pedantic ones) are welcome.

bool unique_chars(std::string &s) {
    if (s.length()>256) return false;
    std::bitset<256> bs;
    for (auto &c:s) {
        if (bs.test(c)) return false;
        bs.set(c);
    }
    return true;
}

EDIT 1:

for (auto &c:s) {         //OLD
for (unsigned char c:s) { //NEW

Reasoning:

1. char can be either signed or unsigned
2. if signed then bs[] can be out of bounds
3. casting to unsigned eliminates issue as negative values will wrap

EDIT 2:

This string is to be made up of characters from the standard ASCII character set, i.e. fitting into a 1 byte char.

Critiques (even pedantic ones) are welcome.

bool unique_chars(std::string &s) {
    if (s.length()>256) return false;
    std::bitset<256> bs;
    for (auto &c:s) {
        if (bs.test(c)) return false;
        bs.set(c);
    }
    return true;
}

EDIT 1:

for (auto &c:s) {         //OLD
for (unsigned char c:s) { //NEW

Reasoning:

1. char can be either signed or unsigned
2. if signed then bs[] can be out of bounds
3. casting to unsigned eliminates issue as negative values will wrap

EDIT 2:

This string is to be made up of characters from the standard ASCII character set, i.e. fitting into a 1 byte char.

EDIT 3:

Renamed function / added test harness with examples. Function parameter changed to const, as string not being modified.

#include <iostream>
#include <bitset>

bool areCharsUnique(const std::string &s) {
    if (s.length()>256) return false;
    std::bitset<256> bs;
    for (unsigned char c:s) {
        if (bs.test(c)) return false;
        bs.set(c);
    }
    return true;
}

int main() {
    std::string s1 = "hi there";
    std::string s2 = "hey man";
    std::cout << areCharsUnique(s1) << std::endl; //0
    std::cout << areCharsUnique(s2) << std::endl; //1
   return 0;   
}

Critiques (even pedantic ones) are welcome.

#include <iostream>
#include <bitset>

bool areCharsUnique(const std::string &s) {
    if (s.length()>256) return false;
    std::bitset<256> bs;
    for (unsigned char c:s) {
        if (bs.test(c)) return false;
        bs.set(c);
    }
    return true;
}

int main() {
    std::string s1 = "hi there";
    std::string s2 = "hey man";
    std::cout << areCharsUnique(s1) << std::endl; //0
    std::cout << areCharsUnique(s2) << std::endl; //1
   return 0;   
}

EDIT 1:

for (auto &c:s) {         //OLD
for (unsigned char c:s) { //NEW

Reasoning:

1. char can be either signed or unsigned
2. if signed then bs[] can be out of bounds
3. casting to unsigned eliminates issue as negative values will wrap

EDIT 2:

This string is to be made up of characters from the standard ASCII character set, i.e. fitting into a 1 byte char.

EDIT 3:

Renamed function / added test harness with examples. Function parameter changed to const, as string not being modified.

Critiques (even pedantic ones) are welcome.

bool unique_chars(std::string &s) {
    if (s.length()>256) return false;
    std::bitset<256> bs;
    for (auto &c:s) {
        if (bs.test(c)) return false;
        bs.set(c);
    }
    return true;
}

EDIT 1:

for (auto &c:s) {         //OLD
for (unsigned char c:s) { //NEW

Reasoning:

1. char can be either signed or unsigned
2. if signed then bs[] can be out of bounds
3. casting to unsigned eliminates issue as negative values will wrap

EDIT 2:

This string is to be made up of characters from the standard ASCII character set, i.e. fitting into a 1 byte char.