How do I insert an integer i into a string? I tried this, but it doesn't work:
for (int i = 0; i < maxFrameBoss1; i++) {
boss1Image[i] = al_load_bitmap("boss1//frame_0" + i + "_delay-0.03s.png");
}
4 Answers
You need to convert i to a string first. Then concatenate the strings. Finally (apparently) get a pointer to char for your al_load_bitmap:
for (int i = 0; i < maxFrameBoss1; i++) {
std::string filename = "boss1//frame_0" + std::to_string(i) + "_delay-0.03s.png";
boss1Image[i] = al_load_bitmap(filename.c_str());
}
3 Comments
Mohammad Kanan
why not leave it implicit ?
std::string filename = "boss1//frame_0" + i + "_delay-0.03s.png";
John
Ok. So it says: 'ALLEGRO_BITMAP *al_load_bitmap(const char *)': cannot convert argument 1 from 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>' to 'const char *'
Jerry Coffin
@MohammadKanan: Because it won't work. You can add an integer to a pointer, so
"boss1//frame_0 + i yields a result--but the result is that pointer advanced by i positions, so if (for example) i = 10, that much basically yields: "me_0". Trying to add that to another string literal won't work.How do I insert an "i" variable into a string.
There is a standard library function to convert an int to a std::string. See http://en.cppreference.com/w/cpp/string/basic_string/to_string.
Use
std::string filename = std::string("boss1//frame_0") + std::to_string(i) + "_delay-0.03s.png";
boss1Image[i] = al_load_bitmap(filename);
If al_load_bitmap cannot use a std::string, use:
std::string filename = std::string("boss1//frame_0") + std::to_string(i) + "_delay-0.03s.png";
boss1Image[i] = al_load_bitmap(filename.c_str());
4 Comments
Justin
I'm a little curious; how would you feel about
al_load_bitmap(("boss1//frame_0" + std::to_string(i) + "_delay-0.03s.png").c_str())?
R Sahu
@Justin, I prefer to use two lines. It's easier to understand and maintain.
John
Ok. Now it says: 'ALLEGRO_BITMAP *al_load_bitmap(const char *)': cannot convert argument 1 from 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>' to 'const char *'
R Sahu
@mmarcin8, looks like you need the second version of my suggested solution.
The easy way to construct strings from arbitrary input types is to use std::ostringstream like so:
for (int i = 0; i < maxFrameBoss1; i++) {
std::ostringstream bitmap_filename_builder;
bitmap_filename_builder << "boss1//frame_0" << i << "_delay-0.03s.png";
boss1Image[i] = al_load_bitmap(bitmap_filename_builder.str().c_str());
}
When using this, take care about the lifetime of the temporarily created std::string variable returned by the std::ostrinsgstream::str() function. The result of the c_str() function may become a dangling pointer after execution of that statement.
Be sure that the function you're calling takes a copy of that c-style string parameter, or just uses it in a strongly sequential manner and doesn't store that pointer as a state elsewhere.
Comments
The easiest solution is to just use std::to_string(i), but that could potentially lead to extra allocations, as std::string cannot know the final size in the intermediate + operations.
Instead, you may want to use absl::StrCat or some other variant:
for (int i = 0; i < maxFrameBoss1; i++) {
std::string filename = absl::StrCat("boss1//frame_0", i, "_delay-0.03s.png");
boss1Image[i] = al_load_bitmap(filename.c_str());
}
This is a relatively small performance point, but the solution is easy enough to be worth mentioning.
#include <string>.