String.Format 和builder.AppendFormat实现代码

 String.Format 实现代码：
public static string Format(IFormatProvider provider, string format, params object[] args){ if ((format == null) || (args == null)) { throw new ArgumentNullException((format == null) ? "format" : "args"); } StringBuilder builder = new StringBuilder(format.Length + (args.Length * 8)); builder.AppendFormat(provider, format, args); return builder.ToString();}

builder.AppendFormat 代码：
public StringBuilder AppendFormat(IFormatProvider provider, string format, params object[] args){ int num3; if ((format == null) || (args == null)) { throw new ArgumentNullException((format == null) ? "format" : "args"); } char[] chArray = format.ToCharArray(0, format.Length); int index = 0; int length = chArray.Length; char ch = '/0'; ICustomFormatter formatter = null; if (provider != null) { formatter = (ICustomFormatter) provider.GetFormat(typeof(ICustomFormatter)); }Label_004E: num3 = index; int num4 = index; while (index < length) { ch = chArray[index]; index++; if (ch == '}') { if ((index < length) && (chArray[index] == '}')) { index++; } else { FormatError(); } } if (ch == '{') { if ((index < length) && (chArray[index] == '{')) { index++; } else { index--; break; } } chArray[num4++] = ch; } if (num4 > num3) { this.Append(chArray, num3, num4 - num3); } if (index == length) { return this; } index++; if (((index == length) || ((ch = chArray[index]) < '0')) || (ch > '9')) { FormatError(); } int num5 = 0; do { num5 = ((num5 * 10) + ch) - 0x30; index++; if (index == length) { FormatError(); } ch = chArray[index]; } while (((ch >= '0') && (ch <= '9')) && (num5 < 0xf4240)); if (num5 >= args.Length) { throw new FormatException(Environment.GetResourceString("Format_IndexOutOfRange")); } while ((index < length) && ((ch = chArray[index]) == ' ')) { index++; } bool flag = false; int num6 = 0; if (ch == ',') { index++; while ((index < length) && (chArray[index] == ' ')) { index++; } if (index == length) { FormatError(); } ch = chArray[index]; if (ch == '-') { flag = true; index++; if (index == length) { FormatError(); } ch = chArray[index]; } if ((ch < '0') || (ch > '9')) { FormatError(); } do { num6 = ((num6 * 10) + ch) - 0x30; index++; if (index == length) { FormatError(); } ch = chArray[index]; } while (((ch >= '0') && (ch <= '9')) && (num6 < 0xf4240)); } while ((index < length) && ((ch = chArray[index]) == ' ')) { index++; } object arg = args[num5]; string str = null; if (ch == ':') { index++; num3 = index; num4 = index; while (true) { if (index == length) { FormatError(); } ch = chArray[index]; index++; switch (ch) { case '{': if ((index < length) && (chArray[index] == '{')) { index++; } else { FormatError(); } break; case '}': if ((index < length) && (chArray[index] == '}')) { index++; } else { index--; if (num4 > num3) { str = new string(chArray, num3, num4 - num3); } goto Label_0253; } break; } chArray[num4++] = ch; } }Label_0253: if (ch != '}') { FormatError(); } index++; string str2 = null; if (formatter != null) { str2 = formatter.Format(str, arg, provider); } if (str2 == null) { if (arg is IFormattable) { str2 = ((IFormattable) arg).ToString(str, provider); } else if (arg != null) { str2 = arg.ToString(); } } if (str2 == null) { str2 = string.Empty; } int repeatCount = num6 - str2.Length; if (!flag && (repeatCount > 0)) { this.Append(' ', repeatCount); } this.Append(str2); if (flag && (repeatCount > 0)) { this.Append(' ', repeatCount); } goto Label_004E;}