Question

I generate a set of data files. As the files are supposed to be readable, they text files (opposed to binary files).

To output information to my files, I used very comfortable std::ofstream object.

In the beginning, when the data to be exported was smaller, the time needed to write to the files was not noticeable. However, as the information to be exported has accumulated, it takes now around 5 minutes to generate them.

As I started being bothered by waiting, my question is obvious: Is there any faster alternative to std::ofstream, please? In case there is faster alternative, will it be worth of rewritting my application? In other words, could the time saved be +50%? Thank you.

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Update:

I was asked to show you my code that generates the above files, so here you are – the most time consuming loop:

ofstream fout;
fout.open(strngCollectiveSourceFileName,ios::out);

fout << "#include \"StdAfx.h\"" << endl;
fout << "#include \"Debug.h\"" << endl;
fout << "#include \"glm.hpp\"" << endl;
fout << "#include \"" << strngCollectiveHeaderFileName.substr( strngCollectiveHeaderFileName.rfind(TEXT("\\")) + 1) << "\"" << endl << endl;

fout << "using namespace glm;" << endl << endl << endl;


for (unsigned int nSprite = 0; nSprite < vpTilesetSprites.size(); nSprite++ )
{
    for(unsigned int nFrameSet = 0; nFrameSet < vpTilesetSprites[nSprite]->vpFrameSets.size(); nFrameSet++)
    {

        // display index definition
        fout << "// Index Definition: " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetLongDescription() << "\n";
        string strngIndexSignature = strngIndexDefinitionSignature;
        strngIndexSignature.replace(strngIndexSignature.find(TEXT("#aIndexArrayName#")), strlen(TEXT("#aIndexArrayName#")), TEXT("a") + vpTilesetSprites[nSprite]->GetObjectName() + vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetFrameSetName() + TEXT("IndexData") );
        strngIndexSignature.replace(strngIndexSignature.find(TEXT("#ClassName#")), strlen(TEXT("#ClassName#")), strngCollectiveArrayClassName );        
        fout << strngIndexSignature << "[4] = {0, 1, 2, 3};\t\t" << "// " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetShortDescription() << ": Index Definition\n\n";


        // display vertex definition
        fout << "// Vertex Definition: " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetLongDescription() << "\n";

        string strngVertexSignature = strngVertexDefinitionSignature;
        strngVertexSignature.replace(strngVertexSignature.find(TEXT("#aVertexArrayName#")), strlen(TEXT("#aVertexArrayName#")), TEXT("a") + vpTilesetSprites[nSprite]->GetObjectName() + vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetFrameSetName() + TEXT("VertexData") );
        strngVertexSignature.replace(strngVertexSignature.find(TEXT("#ClassName#")), strlen(TEXT("#ClassName#")), strngCollectiveArrayClassName );
        fout << strngVertexSignature << "[" << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetFramesCount() << "] =\n";
        fout << "{\n";

        for (int nFrameNo = 0; nFrameNo < vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetFramesCount(); nFrameNo++)
        {
            fout << "\t" << "{{ vec4(" << fixed << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[0].vPosition.fx << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[0].vPosition.fy << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[0].vPosition.fz << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[0].vPosition.fw << "f), vec2(" << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[0].vTextureUV.fu << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[0].vTextureUV.fv << "f) },  // " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetShortDescription() << " vertex 1: vec4(x, y, z, w), vec2(u, v) \n";
            fout << "\t" << " { vec4(" << fixed << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[1].vPosition.fx << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[1].vPosition.fy << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[1].vPosition.fz << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[1].vPosition.fw << "f), vec2(" << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[1].vTextureUV.fu << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[1].vTextureUV.fv << "f) },  // " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetShortDescription() << " vertex 2: vec4(x, y, z, w), vec2(u, v) \n";
            fout << "\t" << " { vec4(" << fixed << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[2].vPosition.fx << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[2].vPosition.fy << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[2].vPosition.fz << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[2].vPosition.fw << "f), vec2(" << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[2].vTextureUV.fu << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[2].vTextureUV.fv << "f) },  // " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetShortDescription() << " vertex 3: vec4(x, y, z, w), vec2(u, v) \n";
            fout << "\t" << " { vec4(" << fixed << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[3].vPosition.fx << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[3].vPosition.fy << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[3].vPosition.fz << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[3].vPosition.fw << "f), vec2(" << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[3].vTextureUV.fu << "f, " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->vpFrames[nFrameNo]->aVertices[3].vTextureUV.fv << "f) }},  // " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetShortDescription() << " vertex 4: vec4(x, y, z, w), vec2(u, v) \n\n";
        }
        fout << "};\n\n\n\n";
    }
}

fout.close();

Answer 1

How are vpTilesetSprites and vpTilesetSprites[nSprite] stored? Are they implemented with lists or arrays? There is a lot of indexed access to them, and if they are list-like structures, you’ll spend a lot of extra time following needless pointers. Ed S.’s comment is right: giving the long indexed temporary variables and linebreaks could make it easier to read, and maybe faster, too:

fout << "// Index Definition: " << vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetLongDescription() << "\n";
string strngIndexSignature = strngIndexDefinitionSignature;
strngIndexSignature.replace(strngIndexSignature.find(TEXT("#aIndexArrayName#")), strlen(TEXT("#aIndexArrayName#")), TEXT("a") + vpTilesetSprites[nSprite]->GetObjectName() + vpTilesetSprites[nSprite]->vpFrameSets[nFrameSet]->GetFrameSetName() + TEXT("IndexData") );
strngIndexSignature.replace(strngIndexSignature.find(TEXT("#ClassName#")), strlen(TEXT("#ClassName#")), strngCollectiveArrayClassName );        

vs

string idxsig = strngIndexDefinitionSignature;
sprite sp = vpTilesetSprites[nSprite];
frameset fs = sp->vpFrameSets[nFrameSet];

fout << "// Index Definition: " << fs->GetLongDescription() << "\n";
idxsig.replace(idxsig.find(TEXT("#aIndexArrayName#")), strlen(TEXT("#aIndexArrayName#")),
    TEXT("a") + sp->GetObjectName() + fs->getFrameSetName() + TEXT("IndexData"));
idxsig.replace(idxsig.find(TEXT("#ClassName#")), strlen(TEXT("#ClassName#")),
    strngCollectiveArrayClassName);

But, the much bigger problem is how you’re using strings as templates; you’re looking for a given text string (and computing the length of your needle string every single time you need it!) over and over again.

Consider this: You’re performing the find and replace operations nSprite * nFrameSet times. Each time through, this loop:

• makes a copy of strngIndexDefinitionSignature
• creates four temporary string objects when concatenating static and dynamic strings
• compute strlen(TEXT("#ClassName#"))
• compute strlen(TEXT("#aIndexArrayName#"))
• find start point of both
• replace both texts with new texts

And that’s just the first four lines of your loop.

Can you replace your strngIndexDefinitionSignature with a format string? I assume it currently looks like this:

"flubber #aIndexArrayName# { blubber } #ClassName# blorp"

If you re-write it like this:

"flubber a %s%sIndexData { blubber } %s blorp"

Then your two find and replace lines can be replaced with:

sprintf(out, index_def_sig, sp->GetObjectName(), fs->getFrameSetName(),
    strngCollectiveArrayClassName);

This would remove two find() operations, two replace() operations, creating and destroying four temporary string objects, a string duplicate that was promptly over-written with two replace() calls, and two strlen() operations that return the same result every time (but aren’t actually needed anyway).

You can then output your string with << as usual. Or, you can change sprintf(3) to fprintf(3), and avoid even the temporary C string.