我目前正在编写一些使用小型微控制器运行的代码，需要实现一个版本的Sprintf（标准库版本太大）。我已经设法创建了一个版本，但我想知道人们对它的看法，以及是否有人可以提出任何改进建议，特别是任何建议让它运行得更快，或者减少代码大小。
目前的功能是：
int sprintf(char *s, const char *format, ...){
char c;
char i;
long n;
char length;
char *string;
va_list a;
va_start(a, format);
while (c = *format++) { //keep going untill the whole string is written to the array, increasing the pointer each loop round
if (c == '%') { //is the next character special
switch (c = *format++) { // move to the next postition to see what to do
case 's': // read a String from the corresponding variable
string = va_arg(a, char*);
i = 0;
while (string[i] != NULL) {
*s++ = string[i];
i++;
}
break;
case 'i': // read an integer from the corresponding variable
n = va_arg(a, int);
if (n > 100000) {
*s++ = IntToAcii(n / 100000 % 10);
}
if (n > 10000) {
*s++ = IntToAcii(n / 10000 % 10);
}
//Deliberately no break, rolls through to case below
case 'c': // read a char from the corresponding variable
if (c == 'c') {
n = va_arg(a, char);
}
if (n > 100) {
*s++ = IntToAcii(n / 100 % 10);
}
if (n > 10) {
*s++ = IntToAcii(n / 10 % 10);
}
*s++ = IntToAcii(n % 10);
break;
case '0': // inserts the number from the variable with padded 0 if it is too small to have a set size
length = *format++;
length -= 0x30;
switch (c = *format++) {
case 'i': // read an int from the corresponding variable (with padding)
n = va_arg(a, int);
if (length > 6) {
length = 6;
}
if (n > 100000) {
*s++ = IntToAcii(n / 100000 % 10);
} else if (length >= 6) {
*s++ = '0';
}
if (n > 10000) {
*s++ = IntToAcii(n / 10000 % 10);
} else if (length >= 5) {
*s++ = '0';
}
if (n > 1000) {
*s++ = IntToAcii(n / 1000 % 10);
} else if (length >= 4) {
*s++ = '0';
}
//Deliberately no break, rolls through to case below
case 'c': // read a char from the corresponding variable (with padding)
if (c == 'c') {
if (length > 3) {
length = 3;
}
n = va_arg(a, char);
}
if (n > 100) {
*s++ = IntToAcii(n / 100 % 10);
} else if (length >= 3) {
*s++ = '0';
}
if (n > 10) {
*s++ = IntToAcii(n / 10 % 10);
} else if (length >= 2) {
*s++ = '0';
}
*s++ = IntToAcii(n % 10);
break;
}
break;
case 'p': // inserts the number from the variable with padded spaces if it is too small to have a set size
length = *format++;
length -= 0x30;
switch (c = *format++) {
case 'l': // read a long from the corresponding variable (with padding)
if (length > 9) {
length = 9;
}
n = va_arg(a, unsigned long);
if (n > 100000000) {
*s++ = IntToAcii(n / 100000000 % 10);
} else if (length >= 9) {
*s++ = ' ';
}
if (n > 10000000) {
*s++ = IntToAcii(n / 10000000 % 10);
} else if (length >= 8) {
*s++ = ' ';
}
if (n > 1000000) {
*s++ = IntToAcii(n / 1000000 % 10);
} else if (length >= 7) {
*s++ = ' ';
}
//Deliberately no break, rolls through to case below
case 'i': // read an int from the corresponding variable (with padding)
if (c == 'i') {
if (length > 6) {
length = 6;
}
n = va_arg(a, int);
}
if (n > 100000) {
*s++ = IntToAcii(n / 100000 % 10);
} else if (length >= 6) {
*s++ = ' ';
}
if (n > 10000) {
*s++ = IntToAcii(n / 10000 % 10);
} else if (length >= 5) {
*s++ = ' ';
}
if (n > 1000) {
*s++ = IntToAcii(n / 1000 % 10);
} else if (length >= 4) {
*s++ = ' ';
}
//Deliberately no break, rolls through to case below
case 'c': // read a char from the corresponding variable (with padding)
if (c == 'c') {
if (length > 3) {
length = 3;
}
n = va_arg(a, char);
}
if (n > 100) {
*s++ = IntToAcii(n / 100 % 10);
} else if (length >= 3) {
*s++ = ' ';
}
if (n > 10) {
*s++ = IntToAcii(n / 10 % 10);
} else if (length >= 2) {
*s++ = ' ';
}
*s++ = IntToAcii(n % 10);
break;
}
}
} else {
*s++ = c; //save the character from the string
}
}
return(1);
}
答案 0 :(得分：2)
这不是一个真正的答案，但它太长，无法适应评论。恕我直言不要试图模仿sprintf 。标准库版本很大，因为它非常强大。如果您需要节省空间，首先要分析您实际需要的内容。我认为有一组函数将整数（并定义你需要的东西：有符号/无符号，大小为1,2,4或8字节）转换为字符串然后连接字符串可以更轻，更简单的编写和测试。
你需要转换指针，浮点数，单个字符吗？如果您对其中一个问题的回答是肯定的，那么只需实现转换功能（不需要单个字符：太琐碎......）。如果你大量使用它们，考虑用汇编语言写它们。但这一切只是基于体验的意见。
答案 1 :(得分：0)
一旦您获得正确的代码，我就会对其进行分析，而不是试图猜测哪些部分正在讨论最多的资源。 （如果我 猜测，我不是，我猜分区/模数是一个值得关注的地方）。