replace_all function in standard C++

replace_all.cc

#include <string>
#include <iostream>
#include <assert.h>

std::string replace_all(const std::string &str, const char *from, const char *to)
{
    std::string result(str);
    std::string::size_type
        index = 0,
        from_len = strlen(from),
        to_len = strlen(to);
    while ((index = result.find(from, index)) != std::string::npos) {
        result.replace(index, from_len, to);
        index += to_len;
    }
    return result;
}

int main(int argc, const char *argv[])
{
    struct str_test_t {
        const char *input;
        const char *from;
        const char *to;
        const char *result;
    } test_strings[] = {
        { "a(wow)b", "wow", "...", "a(...)b" },
        { "Hello world!", " w", "d", "Hellodorld!" },
        { "a\\b\\c", "\\", "\"", "a\"b\"c" },
        { "a\\\\b\\cde\\fg", "\\", "\\\\", "a\\\\\\\\b\\\\cde\\\\fg" },
    };
    for (int i = 0; i < sizeof(test_strings) / sizeof(test_strings[0]); ++i) {
        struct str_test_t s = test_strings[i];
        std::string result = replace_all(s.input, s.from, s.to);
        if (s.result != result) {
            std::cout << "Assertion failed: " << s.result << " != " << result << "\n";
            abort();
        }
    }
    return 0;
}