Microsoft KB Archive/128791

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PRB: Bad Results When %lf Is Format Specifier for Long Double

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Q128791

7.00 | 1.00 1.50 1.51 1.52 MS-DOS | WINDOWS kbtool kbprb - The information in this article applies to: - The Microsoft C Run-time (CRT), included with: - Microsoft C/C++ version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 SYMPTOMS ======== Unpredictable results occur when %lf is used as a format specifier for a long double in functions such as sprintf or printf as in this example: sprintf(chr_buffer, "The value of long double variable is %.3lf ", lng_dbl); CAUSE ===== The format specifier for a long double is Lf, and the format specifier for a double is lf. The format argument tells the function the size and type of the arguments. A long double is 10 bytes and a double is 8 bytes so they need different format specifiers. RESOLUTION ========== Use %Lf as the format specifier for a long double. STATUS ====== This behavior is by design. MORE INFORMATION ================== Sample Code --- /* Compile options needed: none */ #include void main(void) { long double lng_dbl = 2.345; char ch_arr[100]; // Line with the problem resulting from the incorrect specifier sprintf(ch_arr, "%.3lf", lng_dbl); printf("The value of 2.345 is not %s \n", ch_arr); // Line with the correct format specifier sprintf(ch_arr, "%.3Lf ", lng_dbl); printf("The value of 2.345 is %s", ch_arr); } Additional reference words: 7.00 1.00 1.50 1.51 1.52 KBCategory: kbtool kbprb KBSubcategory: CRTIss

Keywords : kb16bitonly

Issue type :

Technology : kbAudDeveloper kbCCompSearch