c++int转string如何补0

我想把当前系统时间转换成string格式,例如20110605123113,但是如果时间不满2位的话不会自动补0,我希望最后得到的string长度是统一的,不知道有什么好办法么.

1、使用sprintf函数即可转换int为string并在前补0。

2、功能: 函数sprintf()用来作格式化的输出。
用法: 此函数调用方式为int sprintf(char *string,char *format,arg_list);
说 明: 函数sprintf()的用法和printf()函数一样,只是sprintf()函数给出第一个参数string(一般为字符数组),然后再调用 outtextxy()函数将串里的字符显示在屏幕上。arg_list为参数表,可有不定个数。通常在绘图方式下输出数字时可调用sprintf()函 数将所要输出的格式送到第一个参数,然后显示输出。
函数名: sprintf
功 能: 送格式化输出到字符串
用 法: int sprintf(char *string, char *farmat [,argument,...]);
程序例:

#include
#include
int main(void)
{
char buffer[80];
sprintf(buffer, "An approximation of Pi is %05d\n", 123);//转换123为"00123"
puts(buffer);
return 0;
}

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第1个回答  2011-06-27
用atoi这个函数,下面的来自msdn
atof, atoi, _atoi64, atol
Convert strings to double (atof), integer (atoi, _atoi64), or long (atol).

double atof( const char *string );

int atoi( const char *string );

__int64 _atoi64( const char *string );

long atol( const char *string );

Routine Required Header Compatibility
atof <math.h> and <stdlib.h> ANSI, Win 95, Win NT
atoi <stdlib.h> ANSI, Win 95, Win NT
_atoi64 <stdlib.h> Win 95, Win NT
atol <stdlib.h> ANSI, Win 95, Win NT

For additional compatibility information, see Compatibility in the Introduction.

Libraries

LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version

Return Value

Each function returns the double, int, __int64 or long value produced by interpreting the input characters as a number. The return value is 0 (for atoi and _atoi64), 0L (for atol), or 0.0 (for atof) if the input cannot be converted to a value of that type. The return value is undefined in case of overflow.

Parameter

string

String to be converted

Remarks

These functions convert a character string to a double-precision floating-point value (atof), an integer value (atoi and _atoi64), or a long integer value (atol). The input string is a sequence of characters that can be interpreted as a numerical value of the specified type. The output value is affected by the setting of the LC_NUMERIC category in the current locale. For more information on the LC_NUMERIC category, see setlocale. The longest string size that atof can handle is 100 characters. The function stops reading the input string at the first character that it cannot recognize as part of a number. This character may be the null character ('\0') terminating the string.

The string argument to atof has the following form:

[whitespace] [sign] [digits] [.digits] [ [sign]digits]

A whitespace consists of space and/or tab characters, which are ignored; sign is either plus (+) or minus ( – ); and digits are one or more decimal digits. If no digits appear before the decimal point, at least one must appear after the decimal point. The decimal digits may be followed by an exponent, which consists of an introductory letter ( d, D, e, or E) and an optionally signed decimal integer.

atoi, _atoi64, and atol do not recognize decimal points or exponents. The string argument for these functions has the form:

[whitespace] [sign]digits

where whitespace, sign, and digits are exactly as described above for atof.

Generic-Text Routine Mappings

TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined
_ttoi atoi atoi _wtoi
_ttol atol atol _wtol

Example

/* ATOF.C: This program shows how numbers stored
* as strings can be converted to numeric values
* using the atof, atoi, and atol functions.
*/

#include <stdlib.h>
#include <stdio.h>

void main( void )
{
char *s; double x; int i; long l;

s = " -2309.12E-15"; /* Test of atof */
x = atof( s );
printf( "atof test: ASCII string: %s\tfloat: %e\n", s, x );

s = "7.8912654773d210"; /* Test of atof */
x = atof( s );
printf( "atof test: ASCII string: %s\tfloat: %e\n", s, x );

s = " -9885 pigs"; /* Test of atoi */
i = atoi( s );
printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );

s = "98854 dollars"; /* Test of atol */
l = atol( s );
printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l );
}

Output

atof test: ASCII string: -2309.12E-15 float: -2.309120e-012
atof test: ASCII string: 7.8912654773d210 float: 7.891265e+210
atoi test: ASCII string: -9885 pigs integer: -9885
atol test: ASCII string: 98854 dollars long: 98854

Data Conversion Routines | Floating-Point Support Routines | Locale Routines

See Also _ecvt, _fcvt, _gcvt, setlocale, strtod, wcstol, strtoul
第2个回答  2011-06-25
louzhu可以试试append。
string str;
str.append(14-str.size(),'0');