将变参格式化到一个string对象中

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该小程序的功能是，仿照sprintf，将变参内容保存到string中。它演示了变参的用法。

/*功能说明：仿照sprintf，将字符串格式化到一个string对象中。实现方式：该例子主要是用来演示变参的用法。使用变参的时候，需要头文件stdarg.h，其使用方式为：va_start(),vsprintf(),va_end()按照顺序的结合。程序调用vsprintf将变参格式化到该临时字符数组中，然后再将此临时字符数组中的数据复制到string对象中。限制条件或者存在的问题：程序在内存的堆中创建了一个临时字符数组，该字符数组的长度为2048个字节。*/#include <iostream>#include <string>#include <cstring>#include <cstdarg>using namespace std;// 仿照sprintf，将字符串格式化到string中。void formatString(string & s, const char *format, ...){size_t strMaxLen = 2048;char * tmp = new char[strMaxLen];memset(tmp, 0x00, strMaxLen);//为string赋值va_list list;va_start(list, format);//size_t len = vsnprintf(tmp, strMaxLen, format, list);size_t len = vsprintf(tmp, format, list);if (len >= strMaxLen){tmp[strMaxLen - 1] = '\0';}va_end(list);s = tmp;delete[] tmp;}// 仿照sprintf，将字符串追加到string中。void appendString(string & s, const char *format, ...){size_t strMaxLen = 2048;char * tmp = new char[strMaxLen];memset(tmp, 0x00, strMaxLen);//为string赋值va_list list;va_start(list, format);//size_t len = vsnprintf(tmp, strMaxLen, format, list);size_t len = vsprintf(tmp, format, list);if (len >= strMaxLen){tmp[strMaxLen - 1] = '\0';}va_end(list);s.append(tmp);delete[] tmp;}int main(int argc, char **argv){cout << "process begin at " << (void*)&main << endl;string str;cout << "strlen is " << str.length() << endl;formatString(str, "Hello, world: %d, %lf  %s", 435, 5462.56 / 54, "man");cout <<"after format:" <<str << endl;appendString(str, "|Hello, world: %d, %lf  %s", 435, 5462.56 / 54, "man");cout <<"after append:"<< str << endl;return 0;}

输出的结果为：

process begin at 01251541
strlen is 0
after format:Hello, world: 435, 101.158519 man
after append:Hello, world: 435, 101.158519 man|Hello, world: 435, 101.158519 man

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