sprintf - 4 useless ascii characters before string

Question

I'm working with visual studio 10, qt addin and opecv library.

What I want to do is to load multiple files using a for-loop:

(I have ui.image_templates_comboBox->currentText() = "cat")

for (int i = 1; i <= 15; i++){
    string currentText = ui.image_templates_comboBox->currentText().toStdString();
    char name[40];
    sprintf(name, "Logos/cat/%s_%d.tif", &currentText, i);
    templ_img [i] = cv::imread( name );

So, I thought this should be working OK, but when I debug it, I hover my mouse above "name" and I notice that there are 4 non-english characters preceding currentText value.

I ask 2 questions:

a) How is it possible to ommit those 4 useless characters? (I typed them as "1234" as this site couldn't display them)

name 0x003a7b04 "Logos/cat/1234cat_1.tif" char [40]

b) It is possible to collapse those 4 lines into 1 using an expression inside imread()?

Given the answers already posted, you can guarantee that all of that information fits in a character array of only 40 bytes? At the very least, make the buffer larger, and not dancing on the knife's edge of a buffer overflow error. — PaulMcKenzie, Jan 02 '15 at 14:48

score 5 · Answer 1 · answered Jan 02 '15 at 14:21

5

You cannot use the address of an std::string where a const char* is expected. They are not the same.

sprintf(name, "Logos/cat/%s_%d.tif", currentText.c_str(), i);

answered Jan 02 '15 at 14:21

nvoigt

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2

This is the danger of using `printf`-style functions in C++ - type checking isn't possible. – Mark Ransom Jan 02 '15 at 14:29
1

`-Wall` switch should prevent this mistake. – Marek R Jan 02 '15 at 14:37
1

Type checking is one issue -- the other obvious one is guaranteeing that the string fits into the `name` array. – PaulMcKenzie Jan 02 '15 at 14:50

score 2 · Accepted Answer · answered Jan 02 '15 at 14:36

You are mixing frameworks to much and you do not understand how sprintf works. Fix it like that:

for (int i = 1; i <= 15; i++){
    QString fileName = QString("Logos/cat/%1_%2.tif")
                       .arg(ui.image_templates_comboBox->currentText())
                       .arg(i);
    templ_img [i] = cv::imread(fileName.toAscii().data()); // or: toLocal8Bit, toLatin1(), toUtf8()

sprintf - 4 useless ascii characters before string

2 Answers2